IPM Vegetable and Fruit Scouting Tips

Cole Crops/ Brassicas:

Continue to scout all fields for caterpillar pests (armyworm, diamondback moth larvae (DBM), and cabbage looper larvae). For fresh-market crops, treat when 20% of the plants are infested during the seedling stage, then 30% infestation till the cupping stage. Use a 5% threshold from early head to harvest for cabbage and Brussels sprouts. For broccoli and cauliflower, use 15% at curd initiation/cupping, then 5% from curd development to harvest.

Good identification as early as possible is important because some products may not be labeled or as effective for all brassicas caterpillar pests. If treatment is needed, adjust your spray pattern so that the spray is getting sideways to the undersides of leaves, particularly when using Bt and other contact materials. Due to resistance development, pyrethroid insecticides (Group 3A) are not recommended for controling DBM. Effective materials should eliminate DBM larvae within 48 hours. Make sure to re-scout treated fields within 3 days to assess the efficacy of the insecticide applications.

Check young plants for flea beetles. Thresholds for flea beetles are 1 per transplant or 5 beetles per 10 plants. They will lay eggs in the soil, and larvae can cause significant root injury. Downy mildew and Alternaria can be problematic in fall brassica crops (cabbage, collards, broccoli, cauliflower, and kale). When the disease first appears, apply a fungicide every 7 to 10 days.

Alium crops:

Scout fall leeks, garlic, or other Allium species from now until the first freeze for Allium leaf miner damage. Egg-laying damage consists of several small round white dots (made by the female’s ovipositor) that appear on the leaf blades. Larvae will live inside the leaves before moving down to the bulbs, where they feed and eventually pupate and overwinter. The feeding damage can open up the foliage and bulb to fungal infections. Row covers can be used to exclude this pest when Alliums are first planted. For organic production, spinosad (Entrust is OMRI-labelled) works well in controlling the larvae. Two or three applications of the insecticide used 2 weeks apart from each other, with the first one coming only after oviposition marks are seen, should offer good control of this pest. The use of a penetrant adjuvant such as neem oil is recommended for better control.

Lima Bean:

Check any late lima bean for soybean looper and stink bugs. Looper activity should decline once nighttime temperatures drop into the low 50s.

Swiss chard, Beets & Spinach:

Check for beet webworm. They fold leaves and cause window-paning feeding damage (fig 1). They also feed on pigweed.

Sweet Corn:

Corn earworm (CEW) numbers have been declining across the state. Cooler night temperatures and shorter day lengths have triggered mature larvae to enter diapause as overwintering pupae.

Spider mites:

Now is a great time to treat weeds growing in and around greenhouses. Winter annual weeds such as chickweed, henbit, dead nettle, and speedwell serve as spider mites and thrip habitats, allowing them to overwinter. Treating now will reduce the possibility of having early-season pest activity on transplants next year.

Emily Zobel, AgFS Agent Dorchester County

When scouting, make sure to check ~10% or 50 plants throughout the whole field when making treatment decisions. Localized infestations can be spot treated to save time and money. For up-to- date chemical recommendations, check the Mid-Atlantic Commercial Vegetable Production Guide (https://go.umd.edu/MidVegGuide). Remember to rotate modes of action and read all labels carefully for rates and restrictions.

Corn Earworm (CEW) 

Activity has increased this past week in Maryland and several surrounding states, with ~20 moths a night in Beltsville, MD. Sweet corn growers should scout fields and consider shortening spray intervals to a 2 to 3-day from green silk through just before harvest. This moth spike is likely coming up from the south due to the recent storms, and moths will likely have greater resistance to pyrethroid than our overwinter population. Galen Divey suggests using Diamides (Vantacor), Blackhawk, Radiant, Lannate, and Entrust (OMRI). Rotate the mode of action when possible. Corn earworm is also a pest of tomato, pepper, snap bean, and lima bean. Visual inspection of the crop to detect eggs and small larvae will help determine pressure and with selecting insecticide materials (Mid-Atlantic Commercial Vegetable Production Guide (https://go.umd.edu/MidVegGuide). Beneficials will feed on the eggs and small larvae. Consider looking for beneficial insects when scouting and using less harmful materials to these natural enemies.

Cole Crops/ Brassicas

Fall cole crops are being transplanted into the field and should be checked for caterpillar and harlequin bugs that may have gotten into high tunnel or greenhouse. For fresh-market cabbage, Brussels sprouts, broccoli, and cauliflower, treat when 20% or more of the plants are infested with any species of caterpillar (imported cabbage worm, cross striped worms, cabbage looper, diamondback moth, or armyworms) during the seedling stage, then 30% infestation from early
vegetative to cupping stage. From early head to harvest, cabbage and Brussels sprouts use a 5% threshold. For broccoli and cauliflower, use 15% at curd initiation/cupping, then 5% from curd development to harvest. If treatment is needed, adjust your spray pattern so that spray is getting sideways to the undersides of leaves, particularly when using Bacillus thuringiensis and contact materials. Due to resistance development, pyrethroid insecticides (Group 3A) are not
recommended for the control of diamondback moths. Remember to rotate between two modes of action within a month and among two different modes of action during the next month.

Melons

Continue to scout melons for aphids, cucumber beetles, spider mites, and rind-feeding lepidopteran worms (yellow striped armyworm, corn earworm, beet armyworm). Beet armyworms and corn earworms are completely or partially resistant to pyrethroids. Any fields treated with broad-spectrum insecticides, such as pyrethroids, should be checked since they can severely reducethese natural enemies causing spider mite outbreaks. If you see large aphid populations, look for beneficial insect activity. If numerous lady beetle, syrphid maggot and lacewing larvae are present, wait and check a few days later as these natural enemies can greatly reduce the aphid population. These infestations can be spotty/localized, so treatment might not be across the whole field.

Cucurbits

Striped cucumber beetle and squash bugs continue to be the main pests. With the humidity and heat, growers should be sure to check for powdery mildew. The threshold is 2 infected leaves/50 leaf samples. For a list of suggested materials, see the 2022/23 Commercial Vegetable Production Recommendations. Jerry Brust recently found squash vine borer in pumpkins. Borer moths lay most of their eggs at the base of pumpkin and squash plants starting in mid-June and going
through the first few weeks of July. Insecticide sprays need to be directed to the base of the plant for several weeks when the moths are active to prevent their larvae from boring into the stem. Once inside the stem, there is very little that can be done to kill the larva. Usually, the best method of control is a cultural one, rotation. Squash vine borer overwinters in the same field they fed in, emerging the following spring/summer and looking for the nearest cucurbit field. Working the field in the fall and spring can help to destroy as many overwintering squash vine borers as possible, reducing next year's population.

Back to the August edition of the Vegetable and Fruit News

July Insect Scouting Tips

Emily Zobel, UME, Dorchester County

Check > 50 plants throughout the whole field when making treatment decisions. Localized infestations can be spot treated to save time and money. For up-to-date chemical recommendations, check the Mid-Atlantic Commercial Vegetable Production Guide. Read all labels carefully for rates and restrictions.

All crops:

Continue to scout for aphids and spider mites. Early detection is critical since these pest populations can quickly explode during hot, dry weather. Adults are small, so the use of a hand lens. Pyrethroid and Carbaryl applications will worsen, so avoid unnecessary pyrethroid applications. Spider mite thresholds are 4 mites per upper canopy leaflet for tomato and 4-8 mites per leaf for eggplant. For cucurbits, treat when 50%of runners show early leaf injury on crown leaves and live mites present.

Cucurbits:

The first generation of striped cucumber beetles are active. When scouting, make sure to check inside the flowers. Kaolin clay can repel beetles but is most effective before beetle populations become high. It should not be used as a rescue treatment. Still, it can be paired with an insecticide application for crops that are susceptible to bacterial wilt. Thresholds are an average of 1 beetle per plant on cantaloupe, cucumber, and watermelon and 5 beetles per plant on squash and pumpkins. Squash bugs are active right now. Thresholds are 1 egg mass per plant. You may need to spray twice to clean them up, about 10 days apart. Eggs are hard to kill with insecticides, so target the nymph stage. Check for rind-feeding pests on melons, such as beet armyworm, yellow-striped armyworm, cabbage loppers, and cucumber beetle. Cucurbit Downy Mildew has been found in surrounding states.

Sweet Corn:

Sample pre-tassel stage for whorl feeders (corn borer, corn earworm, and fall armyworm). Treatment should be applied when 15% early and late whorl infestation and 30% mid-whorl stage. The key is to treat early infestations. When large holes are noticeable, the worms may have left or are too deep in the whorl to reach with an insecticide. David Owens from UD Extension recommends using pyrethroids (only if caught early enough) or Rimon, Intrepid, Intrepid Edge, Avaunt, and the spinosyn class and saving chlorantraniliprole for silk protection later in the season.

Eggplant:

Scout eggplants for defoliation, such as Japanese beetles and Colorado potato beetle (CPB), which can cause heavy defoliation. The threshold for CPB is if you have an average of 4 small larvae or 2 large larvae per plant for plants above 6 inches.

Lima Beans and Snap Beans:

Scout fields for leafhoppers and Mexican bean beetles+. The leafhopper threshold is based on the age of the plant. Pre-bloom, the threshold is an average of 5 per sweep; during bloom, it is 12 adults/nymphs per sweep, and during pod set, it's 25 per adults/nymphs per sweep. Continue to scout for bean leaf beetles and Mexican bean beetles—Control when there is an average of 20% defoliation or 1 beetle per plant.

Potatoes:

Scout fields for Colorado potato beetle, leafhoppers, and aphids. Controls will be needed for aphids if you find 2 aphids per leaf during bloom and 4 aphids per leaf post-bloom. This threshold increases to 10 per leaf at 2 weeks from vine death/kill.

Berries:

Japanese beetles and June beetles are active. Japanese beetles can cause defoliation and may need to be spot treated in some plantings. Control measures for spider mites are not taken until 25% of leaves sampled show the presence of TSSM, but no predator mites are found, OR 30% of leaves sampled show the presence of TSSM, and some predator mites are found.

June Vegetable Insect Scouting Tips

Emily Zobel, Senior Agent Associate, University of Maryland Extension-Dorchester County,

Be sure to check all labels carefully before combining insecticides and herbicides. Thresholds are based on sampling 100 plants (10 plants x 10 locations).

Spider mites can occur in tomato, eggplant, potato, and vine crops such as melons, cucumbers, and other crops. Feeding damage causes leaves to have a yellow-white stippling appearance. Heavy feeding can turn leaves completely pale, dry up, and fall off. They commonly outbreak during hot, dry weather, which also aggravates injury by stressing the plant. However, their populations decline rapidly during periods of heavy rainfall or after overhead irrigation has been used.

Snap beans: Scout for bean leaf beetle, Mexican bean beetle, and potato leafhopper (PLH). Plant leafhopper feeding can cause hopperburn on leaves, reducing photosynthesis and yield. Treated seeds offer protection from plant leafhoppers for about 3 weeks post-planting. The treatment threshold for plant hopper is when adults plus nymphs exceed 100 per 20 sweeps. Bean leaf beetle adults, Mexican bean beetle adults, and larvae chew holes in leaves. The treatment threshold for bean leaf beetle, Mexican bean beetle, is 20% defoliation or 1 beetle per plant.  

Onion: Scout for thrips and feeding damage, which looks like whitish or chlorotic streaks. Prolonged feeding reduces bulb size and increases the incidence of leaf and bulb rots. Immature thrips usually feed on young tissue between the leaf sheaths and stem, while adults feed on more mature tissue. The treatment threshold is an average of 2-4 immatures per leaf. High spray pressures and high gallonages are necessary to ensure good contact between the pest and the chemical. Twin flat fan nozzles result in better coverage than single flat fans.

Eggplant & Potato: Scout for flea beetles and Colorado potato beetles. Adult flea beetle feeding creates small feeding holes that create a shot-hole effect. Treatment thresholds are an average of 2 beetles per plant when plants are less than 3 inches high, an average of 4 beetles per plant when plants are between 3-6 inches high, and an average of 8 per plant when plants are above 6 inches.   

Colorado potato beetle adults and larvae feed on the foliage of solanaceous crops (potato, eggplant, and tomato). They have 1-2 generations per year, and a large population can completely defoliate plants. The treatment threshold is an average of 0.5 adults, 4 small larvae, or 1.5 large larvae per plant. 

Cucurbits:  Scout for aphids, cucumber beetles, and squash bugs. Aphids are found on the undersides of leaves. Examine two runners at 10 sites. If 20 percent of runners or more have live aphids, treatment may be needed. Good coverage of the undersides of leaves is needed for control. Hot, dry weather can cause melon aphid populations to increase rapidly.  Cucurbit crops that are susceptible to bacterial wilt should be protected from cucumber beetles from seedling emergence to the time vines begin to run. Treatment thresholds are an average of >5 beetles per plant when plants are small (>5th leaf stage). The treatment threshold for plants beyond the 4-leaf stage until vines begin to run is when the average beetle densities are 1 per plant.

It is crucial to check 5-10 locations (50+ plants) throughout the field when making treatment decisions. Localized in-festations can be spot treated to save resources, time, and money. For up-to-date chemical recommendations, check the Mid-Atlantic Commercial Vegetable Production Guide or consult your local extension agent.

Melons

As the weather warms up, you will want to start scouting melons for aphids, cucumber beetles, and spider mites since once we get a few consecutive days of warm, sunny weather, populations can explode. For spi-der mites, treatment is warranted when 10-15% of the crown leaves are infested early in the season and when 50% of crown leaves are infested late in the season. The continued use of Sevin or the pyrethroids may result in mite outbreaks. The thresholds in watermelons is an aver-age of 2 adult beetle is found per plant. When applying a insectcde via drip mack sure to pay attention to label guidelines on how much insecticide should be used per 1,000 row feet of drip tape and your given row spacing. The amount will changes depending on how far apart the beds are (5 ft centers use less insecticide per 1,000 feet of drip than 7 ft centers, but there is more drip tape). For early planted cucurbits that are in bloom already consider using Assail over a foliar thiamethoxam or imidacloprid. A couple of diamides are labeled for striped cucumber bee-tle but are best used later in the season when rind worms are also a problem. Assail will not impact the worm com-plex, and the diamides are superb worm insecticides.

Eggplant & Potato

Start scouting for flea beetles and Colorado potato beetles. Adult flea beetle feeding creates small feeding holes that create a shot-hole effect. Treatment thresholds are an average of 2 beetles per plant when plants are less than 3 inches high, an average of 4 beetles per plant when plants are between 3-6 inches high, and an average of 8 per plant when plants are above 6 inches.

Colorado potato beetle adults and larvae feed on the foliage of solanaceous crops (potato, eggplant, and tomato). A treatment should be considered if the number of adults or larvae or defoliation levels reach one of these thresh-olds: 10% defoliation or 25 adult beetles per 50 plants or 4 small larvae per plant or 1.5 large larvae per plant. Threshold for eggplant are based on height. When plants are less than 6” tall: 2 small or 1 large larva per plant. When plants are more than 6” tall: 4 small or 2 large larvae per plant.

Sweet Corn

Sample for cutworms and flea beetles. As a general guideline, treatments should be applied if you find 3% cut plants or 10% leaf feeding. In order to get an accurate estimate of flea beetle populations, fields should be scouted mid-day when beetles are active.

Emily Zobel, Senior Agent Associate - Dorchester County

General Scouting tips

When scouting, check 5-10 locations (50+ plants) throughout the field. Localized infestations can be spot treated to save resources. The threshold is when a pest's population level or the amount of injury present will justify the cost of artificial control measures. If the threshold is approached but not reached, do not apply a pesticide at that time. Instead, wait and re-scout the field in a few days to determine the infestation status since pest populations can decline naturally due to feeding from natural enemies and unfavorable weather conditions. Check the 2022-2023 Mid-Atlantic Commercial Vegetable Production Guide, or consult your local extension agent for current chemical recommendations. Whole season IPM threshold can be found on the IPM Threshold Guide for Vegetable Crops guide (https://extension.umd.edu/resource/ipm-threshold-guide-vegetable-crops)

Greenhouse

Check transplants in greenhouses for signs of aphids and spider mites. Yellow sticky card traps can be placed throughout the greenhouse. Many insects are attracted to the color yellow (thrips are also attracted to the color blue, and blue sticky traps are available). The traps should be placed in a grid-like fashion, with at least one card per 1,000 square feet of production area. Place the cards just above the plant canopy or up to 16 inches above the crop. The cards should be placed in the same position each time to allow an accurate picture of insect activity to emerge. Traps should be changed, and insect counts recorded at least weekly or more often, depending upon the level of the pest population.

Brassica/Cole crops

Scout for flea beetles, diamondback, and imported cabbageworm larvae. For fresh-market cabbage, Brussels sprouts, broccoli and cauliflower, treat when 20% or more of the plants are infested with any species of caterpillar during seedling stage, then 30% infestation from early vegetative to cupping stage. From early head to harvest in cabbage and Brussels sprouts use a 5% threshold. For broccoli and cauliflower, use 15% at curd initiation/cupping, then 5% from curd development to harvest. Spray coverage under the leaves is essential for effective control particularly with Bacillus thuringiensis and contact materials. Avoid using pyrethroids and organophosphates in the springtime since they can negatively affect natural enemies. For flea beetles, treat if the population reaches an average of 1 beetle per transplant or 5 beetles per 10 plants during the cotyledon stage.

Asparagus

Asparagus beetles must be controlled on seedlings, during fern growth, and at harvest. Consider treatment for asparagus beetles if 5-10% of plants are infested with adult beetles, 2% of spears have eggs present with no natural enemies seen, 50-75% of plants have larvae present, or 10% of plants are defoliated. At the end of the growing season, destroy crop residues in and around the field to eliminate overwintering sites and reduce the population for the following year.

Peas

Scout for pea aphids. On small plants, sample for aphids by counting the number of aphids on 10 plants in 10 locations throughout a field. On larger plants, take 10 sweeps in 10 locations. Treatment is recommended if you find 5-10 aphids per plant or 50 or more aphids per sweep. Check labels for application restrictions during bloom.

Strawberries

Check strawberry plants for spider mites, cyclamen mites, and tarnished plant bugs. Spider mite thresholds for fruiting strawberries vary, but a good ballpark is 10-15 mites per leaflet. Cyclamen mites are tiny mites that feed on the growing points leaving deformed leaf tissue and severely stunted plants. Adults and nymphs tarnished plant bug (TPB) feeding causes misshapen fruit and 'button' berries. To scout, shake flower clusters onto plastic or a white surface and count adults and nymphs. University of Massachusetts Amherst has a good scouting guide for them: https://ag.umass.edu/fruit/fact-sheets/strawberry-ipm-tarnished-plant-bug. The action threshold is if you find more than 0.15 nymphs per cluster ( 3 nymphs on 15 clusters, 5 nymphs on 40 clusters, or 6 nymphs on 50 clusters). If this level is reached, control measures can be applied to maintain berry quality and yield before too much damage occurs. Less than that, continue sampling. Pay attention to weedy field edges or filed near alfalfa since this is where TPB overwinter.

Remember to rotate modes of action out every 30 days. Always read the label. See the Mid-Atlantic Commercial Vegetable Production Recommendations Guide for more information (https://go.umd.edu/MidVegGuide).

Cole Crops/ Brassicas

Continue to scout all fields for beet armyworm, fall armyworm, diamond-back moth larvae ((DBM)and cabbage looper larvae. For fresh-market crops treat when 20% of the plants are infested during seedling stage, then 30% infestation from early vegetative to cupping stage. From early head to harvest in cabbage and Brussels sprouts use a 5% threshold. For broccoli and cauliflower, use 15% at curd initiation/cupping, then 5% from curd development to harvest. If treatment is needed make sure to adjust your spray pattern such that spray is getting sideways to the under-sides of leaves, particularly when using Bt and con-tact materials. Due to resistance development, pyrethroid insecticides (Group 3A) are not recommended for control of diamondback moths. Rutger’s is reporting that DBM is not responding to chlorantraniliprole (Coragen) in many parts of the state. It is important to return to treated fields within 2-3 days to assess the efficacy of the insecticide applications. Effective materials should eliminate DBM larvae within 48 hours.

Sweet Corn

Scout any whorl stage sweet corn for fall armyworm (FAW). FAW can infest plants at any growth stage. Injury from newly hatched larvae shows up as “window panes.” As larvae gain size, they begin creating ragged holes in leaves with lots of droppings. FAW can be tough to manage be-cause it is resistant to synthetic pyrethroid insecticides (IRAC 3A). Treat when 15% early whorl infestation, 30% mid whorl, and 15% infestation at tassel push. CEW number are currently active but low across that state, so unless temperatures rise again a 4-5 days spray schedule would be suggested for corn that’s tasseling or silking. Pyrethroid (Group 3A) resistance has been reported in populations of CEW.

Pumpkins and Late Melons:

Scout for cucumber beetles and rind feeding lepidopteran worms, such as melon worms and fall armyworm. Look at the undersides of leaves that have been partially shredded and look at the rinds of pumpkins to determine if they are attacking the fruit.

Remember to rotate modes of action from one spray to another and to rotate modes of action out every 30 days. Be sure to read the label. Not all materials are labeled for all crops, insects, or application methods. See the Mid-Atlantic Commercial Vegetable Production Recommendations Guide for more information (https://go.umd.edu/MidVegGuide).

Cole Crops/ Brassicas

Check seedlings and new transplants of fall brassicas for caterpillar, and harlequin bugs feeding damage. For fresh-market cabbage, Brussels sprouts, broccoli, and cauliflower, treat when 20% or more of the plants are infested with any species of caterpillar (imported cabbage worm, cross striped worms, cabbage looper, diamondback moth, or armyworms) during seedling stage, then 30% infestation from early vegetative to cupping stage. From early head to harvest in cabbage and Brussels sprouts use a 5% threshold. For broccoli and cauliflower, use 15% at curd initiation/cupping, then 5% from curd development to harvest. If treatment is needed make sure to adjust your spray pattern such that spray is getting sideways to the undersides of leaves, particularly when using Bacillus thuringiensis and contact materials. Due to resistance development, pyrethroid insecticides (Group 3A) are not recommended for control of diamondback moths (Fig 1.). Remember to rotate between two modes of action within a 1 month period and among two different modes of action during the next month.

Melons

Continue to scout melons for aphids, cucumber beetles, spider mites and rind-feeding lepidopteran worms (yellow striped armyworm, corn earworm, beet armyworm). Beet armyworm and corn earworm are completely or partially resistant to pyrethroids. Any fields that were treated with broad-spectrum insecticides, such as pyrethroids, should be checked since they can severely reduce these natural enemies causing spider mite outbreaks. If you see large aphid populations, look for beneficial insect activity. If numerous lady beetle, syprhid maggot and lacewing larvae are present, wait and check a few days later as these natural enemies can greatly reduce aphid population. The cool night will also slow them down aphid population growth. These infestations can be spotty/localized so treatment might not be across the whole field.

By Emily Zobel, UME, Dorchester County

Check > 50 plants throughout the whole field when making treatment decisions. Localized infestations can be spot treated to save time and money. For up-to-date chemical recommendations, check the Mid-Atlantic Commercial Vegetable Production Guide. Read all labels carefully for rates and restrictions.

Cucurbits

Continue to scout for aphids, and spider mites. Early detection is critical since these pest populations can quickly explode during hot, dry weather. The first generation of striped cucumber beetles are active. Check for rind feeding pests such as beet armyworm, yellow-striped armyworm, cabbage loppers, and cucumber beetle adults in melon fields.

Sweet Corn

Sample pre-tassel stage for whorl feeders (corn borer, corn earworm, and fall armyworm). Treatment should be applied when 15% of plants are infested with larvae and should be directed into the whorls.

Lima Beans and Snap Beans

Scout fields for aphids, leafhoppers, and spider mites. The leafhopper threshold is an average of 5 per sweep. As soon as pin pods are present, check for plant bugs and stink bug adults and nymphs. As a general guideline, treatment should be considered if you find 15 adults and/or nymphs leafhopper per 50 sweeps. Continue to scout for bean leaf beetles and Mexican bean beetles—Control when there is an aver-age of 20% defoliation or 1 beetle per plant.

Potatoes

Scout fields for Colorado potato beetle, leafhoppers, and aphids. Controls will be needed for green peach aphids if you find 2 aphids per leaf during bloom and 4 aphids per leaf post-bloom. This threshold increases to 10 per leaf at 2 weeks from vine death/kill. If melon aphids are found, the threshold should be reduced by half.

June Vegetable Insect Scouting Tips

Emily Zobel, Senior Agent Associate, University of Maryland Extension-Dorchester County,

Be sure to check all labels carefully before combining insecticides and herbicides. Thresholds are based on sampling 100 plants (10 plants x 10 locations).

Spider mites can occur in tomato, eggplant, potato, and vine crops such as melons, cucumbers, and other crops. Feeding damage causes leaves to have a yellow-white stippling appearance. Heavy feeding can turn leaves completely pale, dry up, and fall off. They commonly outbreak during hot, dry weather, which also aggravates injury by stressing the plant. However, their populations decline rapidly during periods of heavy rainfall or after overhead irrigation has been used.

Snap beans: Scout for bean leaf beetle, Mexican bean beetle, and potato leafhopper (PLH). Plant leafhopper feeding can cause hopperburn on leaves, reducing photosynthesis and yield. Treated seeds offer protection from plant leafhoppers for about 3 weeks post-planting. The treatment threshold for plant hopper is when adults plus nymphs exceed 100 per 20 sweeps. Bean leaf beetle adults, Mexican bean beetle adults, and larvae chew holes in leaves. The treatment threshold for bean leaf beetle, Mexican bean beetle, is 20% defoliation or 1 beetle per plant.  

Onion: Scout for thrips and feeding damage, which looks like whitish or chlorotic streaks. Prolonged feeding reduces bulb size and increases the incidence of leaf and bulb rots. Immature thrips usually feed on young tissue between the leaf sheaths and stem, while adults feed on more mature tissue. The treatment threshold is an average of 2-4 immatures per leaf. High spray pressures and high gallonages are necessary to ensure good contact between the pest and the chemical. Twin flat fan nozzles result in better coverage than single flat fans.

Eggplant & Potato: Scout for flea beetles and Colorado potato beetles. Adult flea beetle feeding creates small feeding holes that create a shot-hole effect. Treatment thresholds are an average of 2 beetles per plant when plants are less than 3 inches high, an average of 4 beetles per plant when plants are between 3-6 inches high, and an average of 8 per plant when plants are above 6 inches.   

Colorado potato beetle adults and larvae feed on the foliage of solanaceous crops (potato, eggplant, and tomato). They have 1-2 generations per year, and a large population can completely defoliate plants. The treatment threshold is an average of 0.5 adults, 4 small larvae, or 1.5 large larvae per plant. 

Cucurbits:  Scout for aphids, cucumber beetles, and squash bugs. Aphids are found on the undersides of leaves. Examine two runners at 10 sites. If 20 percent of runners or more have live aphids, treatment may be needed. Good coverage of the undersides of leaves is needed for control. Hot, dry weather can cause melon aphid populations to increase rapidly.  Cucurbit crops that are susceptible to bacterial wilt should be protected from cucumber beetles from seedling emergence to the time vines begin to run. Treatment thresholds are an average of >5 beetles per plant when plants are small (>5th leaf stage). The treatment threshold for plants beyond the 4-leaf stage until vines begin to run is when the average beetle densities are 1 per plant.

May Vegetable Insect Scouting Update

By Emily Zobel, Ag Agent Dorchester County

It is crucial to check 5-10 locations (50+ plants) throughout the field when making treatment decisions. Localized infestations can be spot treated to save resources, time, and money. For up-to-date chemical recommendations, check the Mid-Atlantic Commercial Vegetable Production Guide or consult your local extension agent.

Spotted Lanternfly Update!

Spotted lanternfly eggs are hatching. Be on the alert when moving equipment or plants out of the quarantine areas. Early instar nymphs are black with domino-like white spots (Fig. 1).

Asparagus:

Continue to scout for asparagus beetles. Feeding by beetles can disfigure spears, and depending on the market, the presence of eggs on the spears can make them unmarketable. When scouting, count adults, eggs, and larvae, and take note of the damage to each plant. Consider treatment if >10% of the spears are infested with beetles (1 or more per plant) or 1-2% have eggs or damage. Treat ferns if 50-75% are infested. Minimize the impact of spear damage on asparagus fields by harvesting asparagus spears every day during the harvest season.

Brassica/Cole crops:

Recently transplanted and newly emerged seedlings of cole crops are at risk of damage from flea beetles. Scout early and consider treating when 50% or more plants show injury and flea beetles are present on plants. Scout fields for imported cabbageworm (ICW) (Fig 2.)and diamondback larvae. With warmer temperatures on the way, these infestations can increase rapidly. When scouting, paying particular attention to the innermost leaves where ICW often feed, consider treating for fresh market cabbage, broccoli and cauliflower if caterpillars are found on 20% or more plants during the seedling stage. Infestations up to 30% may be tolerated from early growth to cupping. On cabbage, once heads begin to form, a 5% threshold should be observed to protect the marketable portion of the plant. For broccoli and cauliflower, use 15% at curd initiation/cupping and 5% from curd development to harvest. For leafy greens such as collards and kale, 10% plants infested is the threshold throughout the season.

Melons:

As the weather warms up, you will want to start scouting melons for aphids, cucumber beetles, and spider mites since once we get a few consecutive days of warm, sunny weather, populations can explode. Consider treating if an average of 2 adult beetle is found per plant. For spider mites, treatment is warranted when 10-15% of the crown leaves are infested early in the season and when 50% of crown leaves are infested late in the season. The continued use of Sevin or the pyrethroids may result in mite outbreaks.

Sweet Corn:

Sample for cutworms and flea beetles. As a general guideline, treatments should be applied if you find 3% cut plants or 10% leaf feeding. In order to get an accurate estimate of flea beetle populations, fields should be scouted mid-day when beetles are active.

Early Spring Vegetable Insect Scouting Tips

Emily Zobel, Senior Agent Associate - Dorchester County

General Scouting tips

When scouting, check 5-10 locations (50+ plants) throughout the field. Localized infestations can be spot treated to save resources. The threshold is when a pest's population level or the amount of injury present will justify the cost of artificial control measures. If the threshold is approached but not reached, do not apply a pesticide at that time. Instead, wait and re-scout the field in a few days to determine the infestation status since pest populations can decline naturally due to feeding from natural enemies and unfavorable weather conditions. For current chemical recommendations, check the 2022-2023 Mid-Atlantic Commercial Vegetable Production Guide or consult your local extension agent.

Brassica crops

Scout for flea beetles, diamondback, and imported cabbageworm larvae. For caterpillars, treat when 30% or more of the plants are infested with any species from early vegetative to cupping stage and from early head to harvest in cabbage. Avoid using pyrethroids and organophosphates in the springtime since they can negatively affect natural enemies. For flea beetles, treat if the population reaches an average of 1 beetle per transplant or 5 beetles per 10 plants during the cotyledon stage.

Asparagus

Asparagus beetles (fig.1, fig 2) need to be controlled on seedlings, during fern growth, and at harvest. Consider treatment for asparagus beetles if 5-10% of plants are infested with adult beetles, 2% of spears have eggs present with no natural enemies seen, 50-75% of plants have larvae present, or 10% of plants are defoliated. At the end of the growing season, destroy crop residues in and around the field to eliminate overwintering sites and reduce the population for the following year.

Peas

Scout for pea aphids on all stages of peas. On small plants, sample for aphids by counting the number of aphids on 10 plants in 10 locations throughout a field. On larger plants, take 10 sweeps in 10 locations. Treatment is recommended if you find 5-10 aphids per plant or 50 or more aphids per sweep. Check labels for application restrictions during bloom.

By Emily Zobel, Extension Educator, University of Maryland Extension-Dorchester County

Read and follow all label requirements. Pay attention to pre-harvest intervals and consider pollinators when making insecticide applications. Please see the 2020-2021 Mid- Atlantic Commercial Vegetable Production Recommendation Guide for more information and control methods.

Please note that some localized corn earworm (CEW), Beet armyworm (BAW), and soybean looper populations have developed resistance to pyrethroids (Group 3A) and that these insecticides should be used with caution and rotated to other insecticide classes within a season.

Sweet Corn

Any late plantings of sweet corn that are silking are at risk for CEW. However, the cooler weather means it will take longer for earworm eggs to hatch, so you can relax your spray schedules a bit.

Cole Crops

Continue to scout for Harlequin bugs, cabbage looper, cabbageworm, diamondback larvae, and yellow striped armyworm. Control needs to be applied before caterpillars move into the head/heart of the plant. The threshold for fresh-market cabbage, Brussels sprouts, broccoli, and cauliflower, treat when 20% or more of the plants are infested with any worm species during the seedling stage, then 30% infestation from early vegetative to cupping stage. From early head to harvest in cabbage and Brussels sprouts, use a 5% threshold. For broccoli and cauliflower, use 15% at curd initiation/cupping, then 5% from curd development to harvest. Spray coverage under the leaves is essential for effective control.

Spinach

Scout for aphids, beet webworm, and BAW. Beet webworm larvae will fold over leaves and will wriggle violently when removed from their shelters. They are narrow, translucent green with many dark spots, while BAW are a dull green and have a small black spot above their second pair of legs behind the head.

Lima and Snap Beans

Continue to scout for stinkbugs, tarnished plant bugs (TPB), soybean looper, and CEW. The threshold for TPB is when the number of adults and nymphs exceeds 15 per 50 sweeps from the pin pod stage until harvest. The threshold for stinkbugs is when the number of adults and nymphs exceeds 7 per 50 sweeps during pod development. In snap beans, you should also check for corn borer and BAW. For lima beans, treat when CEW populations exceed 1 per 6 ft. of row.

As field operations begin to end, it is time to think about cleaning up fields, high tunnels, and greenhouse houses. Good sanitation practice in the fall can reduce the pest populations and disease pressure next year.

By David Owens, Extension Entomologist, University of Delaware

Sweet Corn

Trap counts are fluctuating quite a bit, with some locations higher and others fairly low. This time of year, and particularly with the hot weather we have had, we have had even low trap counts result in a large percentage of damaged ears in untreated check plots. If the daily temperature is above 82 degrees, I advise that spray schedules be tightened 1 day.

Brassicas

Fall brassicas are either just transplanted or soon to be transplanted. Scout seedlings and new transplants for worm damage. Active worms include the various armyworm species in addition to imported cabbage worm, cabbage looper, and diamondback moth. Thresholds for young plants is 20% infestation. Adjust your spray pattern such that spray is getting sideways to the undersides of leaves. Use adjuvants to help spread the droplet out on the waxy leaf surfaces. If using Radiant or a diamide (Coragen, Exirel, Harvanta), do not use a sticker. As much as possible, use a treatment window approach alternating among two modes of action during the first generation (roughly 30 days) followed by completely different modes of action. Save broad-spectrum materials (Lannate, Orthene, Dibrom, pyrethroids) for later in the season. I have heard that the combination of a pyrethroid + organophosphate can result in some synergism for certain pests, but not sure if this holds true for diamondback moth. Also, check your labels to ensure that your selected insecticide is indeed labeled for the particular crop. Many labels exclude certain cole crops. For example, Orthene is only labeled for Brussels sprouts and cauliflower.

Tomato

Corn earworm and yellow striped armyworm are active in tomatoes, and I have seen quite a few worm damaged tomatoes recently. Use high water volume, high pressure, and multiple nozzles aimed at the sides of the row to ensure good coverage. We have a plethora of ‘worm’ materials labeled for tomato, including Entrust and Radiant, Proclaim, Bt (best on small worms but has very little residual), Rimon, Intrepid, Avaunt, and diamides Coragen and Exirel). Stink bugs and leaf footed bugs are also a threat in tomato, if you have to battle them, there are several good premix options that combine a pyrethroid and a neonicotinoid. The neonic component will not affect worms. Among the pyrethroids, bifenthrin is generally thought to be the best for stink bugs, while recent tests in sweet corn show beta cyfluthrin to be a good pyrethroid for corn earworm. Venom and Scorpion are also very effective stink bug products, but will not target worms. The vegetable guide also lists Voliam Flexi which has a neonic and a dimaide.

Spider Mites

Spider mites continue to be active in vegetable fields. They can be pretty hard to dislodge in vegetables on account of frequent fungicide applications and broad-spectrum insecticides targeting other pests. Rotate among product modes of action, use high pressure, and an appropriate adjuvant for the material (no stickers or ‘sticky’ fungicides for translaminar products). Some products take longer to result in a mite population decrease than others.

Cucurbits

Continue to scout for aphids, cucumber beetles and spider mites. Early detection is critical since these pest populations can quickly explode during hot, dry weather. Watch for rind feeding pests such as beet armyworm, yellow-striped armyworm, cabbage loppers, and cucumber beetle adults in melon fields.

Sweet Corn

Sample pre-tassel stage for whorl feeders (corn borer, corn earworm, and fall armyworm). Treatment should be applied when 15% of plants are infested with larvae and should be directed into the whorls.

Lima Beans and Snap Beans 

Scout fields for aphids, leafhoppers, and spider mites. The leafhopper threshold is an average of 5 per sweep. As soon as pin pods are present, check for plant bugs and stink bug adults and nymphs. As a general guideline, treatment should be considered if you find 15 adults and/or nymphs leafhopper per 50 sweeps. Continue to scout for bean leaf beetles and Mexican bean beetles—Control when there is an average of 20% defoliation or 1 beetle per plant.

Potatoes

Scout fields for Colorado potato beetle, leafhoppers, and aphids. Controls will be needed for green peach aphids if you find 2 aphids per leaf during bloom and 4 aphids per leaf post-bloom. This threshold increases to 10 per leaf at 2 weeks from vine death/kill. If melon aphids are found, the threshold should be reduced by half.

Cucurbits

Scout for aphids, cucumber beetles, and spider mites. Treatment should be applied for aphids when 20% of runners/plants are infested with 5 aphids per leaf. Spider mite activity will increase with the hot weather and can double within a few days if not controlled. The treatment threshold for spider mites is 20-30% infested crowns with 1-2 mites per leaf. The threshold for cucumber beetles is an average of 1 beetle per plant in cucumbers, melons, Hubbard and butternut squash, and younger pumpkins, and average of 5 cucumber beetles per plant in watermelon, other varieties of squash, and older pumpkins. When fields are blooming, it is important to consider pollinators when making an insecticide application.

Solanaceae

Scout for Colorado potato beetles (CPB), flea beetles, and spider mites. Treatment threshold for CPB is 25 adult beetles per 50 plants, and defoliation has reached the 10% level on potatoes, or an average of 4 small larvae per plant or 1.5 large larvae per plant. CPB populations readily develop insecticide resistance so rotating between IRAC groups is crucial. See the Mid-Atlantic Commercial Vegetable Production Guide for options for use in a rotation. For eggplant, treat when the average is 1.5 adults per plant or 2 larvae (any size) for plants under 6 inches or 4 small or 2 large larvae per plant when above 6 inches.

Sweet Corn

Continue to scout for cutworms and flea beetles. As a general guideline, treatments should be applied if you find 3% cut plants or 10% leaf feeding by cutworms. Treat if 5% of the plants are infested with flea beetles. Scout whorls through pre-tassel stage sweet corn for corn borers and corn earworms. A treatment should be applied if 15% of the plants are infested.

Brassica

Scout for flea beetles, diamondback, and imported cabbageworm larvae. For flea beetles, treat if the population reaches an average of 1 beetle per transplant or 5 beetles per 10 plants during the cotyledon stage. For caterpillars, the threshold is based on the plant growth stage. The threshold is when 20% of plants are infested with any species during the seedling stage, then 30% infestation from early vegetative to cupping stage. For cabbage, use a 5% threshold from early head to harvest. For broccoli and cauliflower, use 15% at curd initiation/cupping, then 5% from curd development to harvest. Due to resistance development, pyrethroid< insecticides (Group 3A) are not recommended to control Diamondback Moths or beet armyworm control.

Cucurbits

Scout for aphids, cucumber beetles, and spider mites. Treatment should be applied for aphids when 20% of runners are infested with 5 aphids per leaf. The threshold for spider mites is 20-30% infested crowns with 1-2 mites per leaf. The threshold for cucumber beetles is an average of 1 beetle per plant in cucumbers, melons, Hubbard and butternut squash, and younger pumpkins, and average of 5 cucumber beetles per plant in watermelon, other varieties of squash, and older pumpkins.

Solanaceae

Overwinter Colorado potato beetle adults will be emerging soon. Treatment is not needed for adults until you find 25 beetles per 50 plants, and defoliation has reached the 10% level on potatoes. Once larvae are detected, the threshold is 4 small larvae per plant or 1.5 large larvae per plant. There are non-neonicotinoid options available for use in a rotation to ease selection pressure off of neonicotinoids (see Mid-Atlantic Commercial Vegetable Production Guide). For eggplant, treat when the average is 1.5 adults per plant or 2 larvae (any size) for plants under 6 inches or 4 small or 2 large larvae per plant when above 6 inches.

Sweet Corn

Check for cutworms and flea beetles. As a general guideline, treatments should be applied if you find 3% cut plants or 10% leaf feeding by cutworms. Fields should be scouted mid-day when flea beetles are active. Treat if 5% of the plants are infested with beetles. Be sure to also watch for corn borer larvae in the whorls of the earliest planted fields. A treatment should be applied if 15% of the plants are infested.

General Scouting tips

When scouting, check 5-10 locations (50+ plants) throughout the field. Localized infestations can be spot treated to save resources. The threshold is when a pest's population level or the amount of injury present will justify the cost of artificial control measures. If the threshold is approached but not reached, do not apply a pesticide at that time. Instead, wait and rescout the field in a few days to determine the infestation status since pest populations can decline naturally due to feeding from natural enemies and unfavorable weather conditions. For current chemical recommendations, check the Mid-Atlantic Commercial Vegetable Production Guide or consult your local extension agent.

Brassica crops

Scout for flea beetles, diamondback, and imported cabbageworm larvae. For caterpillars, treat when 30% or more of the plants are infested with any species from early vegetative to cupping stage and from early head to harvest in cabbage. Avoid using pyrethroids and organophosphates in the springtime since they can negatively affect natural enemies. For flea beetles, treat if the population reaches an average of 1 beetle per transplant or 5 beetles per 10 plants during the cotyledon stage.

Asparagus

Asparagus beetles need to be controlled on seedlings, during fern growth, and at harvest. Consider treatment for asparagus beetles if 5-10% of plants are infested with adult beetles, 2% of spears have eggs present with no natural enemies seen, 50-75% of plants have larvae present, or 10% of plants are defoliated. At the end of the growing season, destroy crop residues in and around the field to eliminate overwintering sites and reduce the population for the following year.

Strawberry

Scout for two-spotted spider mites by checking 10 leaflets per acre. A hand lens is highly recommended. Spider mite damage that occurs before fruiting can reduce yield. Before fruiting, the threshold is 5 mites per leaflet, but thresholds increase to 20 spider mites per leaflet once berry harvest begins. If treating when plants are in bloom, be mindful of pollinators since poor pollination can lead to misshapen berries. Organic growers should be vigilant because predatory mites and horticultural oils take longer to suppress two-spotted spider mite populations and may need to be applied multiple times.

Peas

Scout for pea aphids on all stages of peas. On small plants, sample for aphids by counting the number of aphids on 10 plants in 10 locations throughout a field. On larger plants, take 10 sweeps in 10 locations. Treatment is recommended if you find 5-10 aphids per plant or 50 or more aphids per sweep. Check labels for application restrictions during bloom.