High Tunnel

A list of meetings for Urban Agriculture growers.

Over the past few weeks we have seen several greenhouse (GH) and high tunnel (HT) vegetable (basil and tomato mostly, but also lettuce, pepper and spinach) operations from around Maryland having problems with thrips.

High tunnels (HTs) are up and running now and we usually do not see many pest problems early on, but there are some potential problems that could develop later in the season that get their start now. One potential problem is when the HT was not cleaned up after the previous year’s crop was finished. Many of these are old tomato plantings, most of which had their plastic, stakes and drip-tape removed but the plants were left to rot in the HT over the winter.

Over the last three months a few early season high tunnel operations on the Eastern Shore were having problems with some of their seedlings and leaf crops. Crops like spinach would have ‘whitening’ and then browning and eventually dead margins of their leaves while seedlings would collapse. The problem was found to be ‘red legged winter mites’ Penthaleus dorsalis, which is a new pest in vegetables and herbs for us (fig 1).

Because of the bright sunny days we have had in the past 3-4 weeks as well as higher temperatures lately vegetables in high tunnels (HT) are highly susceptible to thrips and two spotted spider mite infestations because of the hot dry conditions.

This week I saw several high tunnel tomatoes and cucumbers with moderate to severe two spotted spider mite (TSSM) Tetranychus urticae infestations (fig. 1). These pests vary in color from white to yellow to red. Mites feed by sucking chlorophyll from the plant, which at first appears as small white or yellow marks on the top surface of the leaf (fig. 2). This damage may look like other problems early on and because the mites are difficult to see on the underside of the leaf at this stage of damage their build-up can go unnoticed. The feeding damage then progresses to loss of chlorophyll, yellowing, browning (fig. 3) and eventual death of the leaves or whole plant.

Over the years high tunnel (HT) production of vegetables have enabled growers to extend their vegetable production time by 3-5 months. Producing earlier and later season vegetables compared with field production. Though at times it seems HT vegetables have fewer insect problems this is not true and certain pests need to be watched for and anticipated.

Fruit and Vegetable News, Volume 13, Issue 1 (April, 2022). Topic in this issue are: Check for Allium leaf miner in onions and leeks over the next few weeks, Edema problem in high tunnel tomatoes, Using Plant Growth Regulators to Improve Apple Return Bloom, Botryis Fruit Rot (Gray Mold) and Crown Rot in Strawberries, Spring Pest Scouting in Strawberries, and Early Spring Vegetable Insect Scouting Tips.

I recently received an inquiry from a high tunnel grower about unusual symptoms on tomato leaves.