Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
While there will still be hot days ahead, late summer and early fall bring different challenges and opportunities for vegetable growers. The following are some considerations at this time of year:
● The day length is getting shorter each day and there is less heat accumulated during the day. We have passed the latest planting dates for most summer planted – fall harvested crops to go to successful harvest. A good example is with cucumbers where a 2-3 day planting difference in early August (between August 7 and August 10 for example) will mean the difference between a successful crop and a crop that will not mature in time or that will have low yields. Remember that you are up against the first frosts with many of these crops. There is still time however for many of our frost tolerant crops. Greens, earlier maturing broccoli, spinach, and lettuce for harvest in leaf stage can all be planted through the end of the month for fall harvest.
● Extending harvest seasons is a consideration, especially for smaller growers who sell directly. Floating row covers, low tunnels, and high tunnels are all tools to use for frost protecting sensitive crops (such as a late crop of tomatoes) and for carrying cold season crops into the winter and sometimes over the winter. Older methods such as field storing root crops (think parsnips, turnips, carrots) using mulches for later digging can still be employed.
● Late summer and fall planted overwintering crops will be planted over the next 2 months. This includes plasticulture strawberries, spinach, and garlic. However, there are many other vegetable crops that can be successfully overwintered, especially vegetables in the mustard family and onion family and even some cold hardy legumes.
● Cooler nights and lower duration of high temperatures during the day helps to maintain pod set on snap bean and lima bean crops that will be harvested in September through mid-October. This year has been particularly hard on bean crops maturing in July and August.
● Irrigation management becomes less of a challenge for fall crops because evapotranspiration is reduced. Attention should be paid so as not to over-irrigate as the late season progresses to avoid disease problems.
● Late summer and early autumn brings new challenges in regards to pests. This is the time of the year when we see peaks of many insect pests (such as corn earworm), migratory insect populations that have arrived or will arrive in high numbers, and late season insects in higher numbers. With the lower temperatures and longer nights, dews are heavier, often leading to increased disease pressure and the appearance of late season diseases. Throw in a hurricane or tropical storm during this period it can be a recipe for disaster in some vegetable crops.
● This is also the time of year when growers should be planting cover crops, windbreaks, overwintering biofumigant crops, and overwintering legumes for nitrogen sources where next year’s vegetables will be planted. For a review of these options see the WCU article titled Late Summer and Fall Cover Crops for Vegetable Ground in WCU 17:24. Good rotations are critical for vegetable crop production and planning should start now.