A number of introduced parasites have been instrumental in keeping cereal leaf beetle populations below economic damage levels. Also, favorable planting dates may help suppress populations. Wheat planted early in the fall immediately after the Hessian fly-free date will be more advanced in growth the next spring than late-planted small grains. These early plantings will be less attractive to and more tolerant of the beetles when they peak in the spring. Cereal leaf beetle infestations on spring-planted oats cannot be avoided by means of an early planting date. Generally, barley is more advanced in maturity and thus less attractive when beetles are active.
Scouting should begin in early April as soon as adult beetles are observed. Use the adult abundance in each field as an indicator of potential egg pressure. Samples should be taken at a minimum of 10 random sites in the interior of each field (avoid the edges). At each site, 10 tillers (stems) should be examined to count the number of eggs and larvae. This will result in 100 tillers (stems) per field being examined. Eggs may be on the leaves near the ground. If the population consists mainly of eggs, then schedule field visits at a later date when greater than 50 percent of the immatures are larvae. Cereal leaf beetle is often unevenly distributed in the field, so it may be necessary to subdivide the field into two or more parts and sample each part as an individual field.
All fields that are not treated early should still be scouted for cereal leaf beetle larvae, as well as other insect pests. Later in April or early May, make detailed counts of larvae at 10 sites spread throughout the field. At each site, select a spot at random and carefully delineate the stems of a 6- to 8-inch section of a single row. Examine all the leaf blades, visually estimate the amount of defoliation, count the number of larvae, note the average larval size, and then count the number of stems in the delineated row section. Tally the total number of larvae and stems examined, and compute the average count of larvae per stem.
Damage can build up quickly, often in as little as 5 days, after larvae become large and high temperatures make the insects very active. Leaf feeding reduces the plant's ability to produce photosynthates and limits reproductive growth, particularly if the upper leaves are destroyed. Yields can be reduced by 45 percent when defoliation is 100 percent early in the heading period. Later damage, late in the grain-fill period, does not have a great impact. Keep in mind that the three stem leaves (flag leaf and two leaves below) all contribute to filling grain heads and achieving favorable grain test weight. In fact, the two lower stem leaves are about as important as the flag leaf.
An earlier-triggered threshold is now recommended to allow growers more lead time to take action and apply insecticides together with fungicides to share the application cost. The threshold is 25 or more eggs and/or small larvae per 100 tillers (or one per every four tillers). The orange-brown eggs are easy to find on the upper surface of the leaves. They are shaped like little cucumbers deposited singly or in chains of two or three close to the midrib. Treatment is suggested when the egg threshold is reached and more than 50 percent of the sample count consists of larvae - that is, after 50 percent egg hatch. This decisionmaking strategy works only if a good representative sample estimate of the egg density is obtained and growers wait until 50 percent of the eggs have hatched, at which time most eggs have been laid for the season. If the tendency is to focus on hot spots that exceed the threshold, then fields will be over-treated.
The concern about an early treatment strategy is that growers will automatically treat preventively and overuse insecticides. This can lead to an aphid problem by removing valuable predators, disrupt parasites of the cereal leaf beetle, and add unnecessary cost. If implemented properly, making the spray decision early can almost totally prevent defoliation, often allows the insecticide to be applied together with fungicides to share the application cost, and will not result in more fields treated than would ordinarily be treated later using a larval-based threshold. Use the egg/larval threshold with care and try to apply it to the high management fields only, that is, those that have a yield potential of greater than 60 bushels per acre. Also, avoid using insecticides at top-dress times because these applications are too early in relation to cereal leaf beetle movement into grain fields.
The cereal leaf beetle has a tendency to seek out the sparse wheat fields with the lowest yield potential. It may not be cost-efficient to apply early season controls in these fields, even though egg/larval densities exceed the threshold. In these situations, wait to see how well the crop responds to the nitrogen applications and then evaluate the larval infestation and the economics of treatment. Avoid spraying sparse plantings if possible because they serve as nurseries to increase populations of parasites that will help control the cereal leaf beetles next year.
If fields are not treated early using the egg/larval threshold, insecticidal control is suggested if larval density averages more than 50 per 100 tillers, defoliation is more than 10 percent, and most larvae are still young enough to cause additional injury. Once wheat reaches the hard dough stage, beetle damage has little effect on the yield and thus controls are no longer required.
You are viewing records 1 - 5 of 6. Next 1 Records| Insecticide and formulation | Rate of active ingredient per acre | Rate of formulation per acre | Time lmits: Days before harvest | Remarks |
|---|---|---|---|---|
| carbaryl (Sevin XLR Plus) |
2.0 pt | 21 | Restricted Use: Wheat Only. | |
| lambdacyhalothrin (Lambda-Cy 1EC) |
0.02-0.03 lb | 2.56-3.84 fl oz | 30 | Restricted Use: Barley, oats, rye and wheat. |
| lambdacyhalothrin (Warrior II) |
0.02-0.03 lb | 1.28-1.92 oz | 30 | Restricted Use: Barley, oats, rye and wheat. |
| methomyl (Lannate 2.4LV) |
0.23-0.45 lb | 0.75-1.5 pt | 7 | Restricted Use: Barley, oats, rye and wheat. |
| zeta-cypermethrin (Mustang MAX 0.8EC) |
0.011-0.025 lb | 1.76-4.0 oz | 14 | Restricted Use: Wheat and Triticale. |
