High Tunnel

Last week Gordon Johnson had an article about exhaust problems for greenhouse transplants. In Maryland we have seen a few problems with ethylene interactions with tomatoes in high tunnels. Ethylene (C2H4) occurs in trace amounts in gasoline and natural gas and is produced when these substances are burned. It also is present in wood and tobacco smoke.

Last week Gordon Johnson had an article talking about cold damage to peas and there also has been some cold damage and weather induced damage to vegetables in high tunnels and greenhouses.

There have been several reports of odd looking damage to watermelon transplants being grown in greenhouses these past couple of weeks. The damage does not appear to be cold damage per se, but more of a strange environmental/weather one. Watermelon transplants, along with some other vegetables, began showing dark pitted lesions on their cotyledons (fig. 1).

Over the last month I have received reports from high tunnel (HT) growers that were seeing flower abscission due to poor pollination in their tomatoes (fig. 1). Some of these reports were a few weeks ago and others were just this past week. There are unfortunately several factors that can cause poor pollination in tomatoes.

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.

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.

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).

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 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 an Excellent Tool for Organic Production