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Penn State professor lists concerns with high tunnels

By DOROTHY NOBLE
AFP Correspondent

STATE COLLEGE, Pa. — At this year’s Pennsylvania Association for Sustainable Agriculture Farming for the Future Conference, Michael D. Orzolek, Penn State vegetable crops professor, called attention to problems that occur in high tunnels.
Growers were urged to dedicate time to learn about pests, eliminate or minimize broad spectrum pesticides, scout, locate reliable and helpful suppliers and identify specific pests — all keys to successful high tunnel management, Orzolek said.
Orzolek, who is the director of the university’s Center for Plasticulture, explained how typical problems develop and suggested management techniques to deal with them.
Start with healthy plants, he urged.
Next, scout weekly and observe any trends. Some issues can be more prevalent in high tunnels and fast action can prevent or deter future difficulties.
Nutrition problems can be more common. Professor Orlozek advised tissue testing to determine if a nutritional deficiency exists. If the tissue test shows no deficiency, look for root problems such as nematodes.
The elevated humidity in high tunnels affects the potential for some diseases, including powdery mildew. Using resistant varieties and increasing ventilation within the tunnel should be considered.
Rotating crops in the tunnels helps prevent disease.
Dr. Orzolek recommended observing the field crops for signs of potential tunnel problems. Often, a serious outbreak of blight or mildew occurs in the field first, then enters the high tunnels.
Don’t let weeds reach the flowering stage, he told listeners. Lambsquarters and pigweed particularly lead to disease problems.
Eliminating weeds around the baseboards of tunnels discourages the hosts. When siting tunnels, Dr. Orzolek suggested choosing a place with few, if any, perennial weeds. He related an incident of thistle, which took two days to pull.
Weeds also harbor disease-spreading insects plus those that savor crops.
Because of their high relative value, high yield and higher prices when marketed early, tomatoes are the number one crop for high tunnels, Orzolek said, and advised planting disease resistant varieties, or transplants grafted onto disease-resistant rootstock.
In Penn State’s high tunnels Dr. Orzolek has grown determinate varieties — varieties that ripen all their fruit in a short time fram — without staking. With determinate tomato varieties, multiple planting dates could be considered.
In delineating the problems with tomatoes, he noted that plants will abort flowers at temperatures at or above 90 degrees.
At temperatures below 50 degrees, catfacing will occur.
Orzolek recommended row covers or portable heaters in cold weather situations.
Both temperature problems will correct themselves when temperatures fall into the proper range, typically 60 to 85 degrees.
In any event, ventilation must be manipulated in high tunnels.
Poor pollination also leads to misshapen fruit, including catfacing, and poor fruit set. Excessive humidity is often a factor. Shaking the vines aids pollination.
Pests common in greenhouses plague high tunnels as well. Watch for whiteflies, thrips and an assortment of potato, green, peach and melon aphids.
Cupping and rolling of the leaves signals aphids or water stress, calling for better biocontrols and irrigation management.
Spotted spider mites can be problematic on tomatoes, peppers and eggplant.
Symptoms include stippling, yellowing and white leaves due to the chlorophyll loss from insect feeding. Webbing indicates a serious infestation.
Uneven ripening, such as blotchy fruit, yellow shoulder, graywall or internal whitening can result from low potassium, heavy fruit load, excessive moisture and lower light and temperatures toward the end of the season.