High Tunnel

A root disease that is most commonly associated with potato has turned up on tomato in a high tunnel last week. This disease goes by the delightful name of black dot root rot. The causal agent is Colletotrichum coccodes, which also causes anthracnose fruit rot on tomato (sunken, water-soaked, circular lesions).

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.

An odd problem was seen in tomato plants being grown for harvest in a greenhouse that showed blister- or callus-like growths usually along veins that first appeared on the underside of older leaves (fig. 1). Leaves also showed unusual curling and other odd distortions on the top side of the leaf (fig. 2).

A list of meetings for Urban Agriculture growers.

If you had plants in high tunnel this season that were showing drought and salt stress in the form of poor growth, thin canopy, excessive leaf drop, poor fruit set, poor yields, necrotic leaf margins, especially on older leaves that can curl, then you might want to consider testing your soil for high soluble salts. These excess soluble salts often come from compost, manure, or fertilizers frequently applied without sufficient water (rain) to leach them through the soil. High soluble salt levels in the soil can harm crops via drought stress in several ways. First, they can draw water away from plant roots resulting in wilted foliage and damaged roots (fig. 1). The plant roots can also absorb the excess soluble salts in the soil but cannot metabolize them. The soluble salts enter the roots and are moved through the water-conducting tubes to the leaves, where the water evapotranspires, gradually concentrating the salts to toxic levels.

High tunnels (or hoop houses) extend the growing season for specialty crops. This article will help growers learn how to get the most out of their high tunnel by adopting best management practices for temperature management, soil and growing media monitoring, safety considerations, pest management, and crop selection.

I know growers are very aware that they should clean up their vegetable fields and high tunnel (HT) of old crops and weeds during the off-season. I also know that growers have many other things that need to be done during this time and they can’t quite get to the cleaning. But spending some time now thoroughly cleaning up a high tunnel that is no longer in production rather than letting it sit over the winter will vastly improve your pest problems for the next year.

Over the years several high tunnel (HT) growers have complained to me about how after 4-5 years of growing various vegetables (although tomatoes were the most grown) in their high tunnel they are seeing poorer yields and ‘unthrifty plants’. This seems puzzling because they have put a great deal of compost in their HT and the soil looks great. The problem I think is high soluble salts in the soil which will damage overall plant fitness and yield.

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.

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).