The old saying that an ounce of prevention is worth a pound of cure is probably a conservative estimate. That sure is the case when it comes to managing insects, weeds and diseases on vegetable farms, and especially on organic farms, where the cures (read: organic pesticides) tend to be relatively few, and relatively expensive.
End-of-season pest prevention comes in several flavors: sanitation, crop rotation, record keeping, and soil stewardship. None of these may seem mouth-watering (because they donít generate cash in the near term) but delayed gratification can be a good thing. Next year, and in years to come, youíll reap the rewards of a good management menu this fall.
Sanitation means cleaning up the fields and greenhouses. Plowing, disking or otherwise incorporating residues to speed their decomposition in the field can limit the ability of many insect pests to over-winter. Sanitation can also reduce the amount of time that some insect pests have to store up winter food by feeding on crop residues. Removal or turning under rotting fruits and foliage can prevent some diseases from proliferating, too. If weeds are present, putting them down before they set seed makes good sense. Many annual weeds can produce tens of thousands of seeds per plant if allowed to mature.
In greenhouses and high tunnels, sanitation provides an added benefit. Not only can over-wintering sites for pests be removed, but a clean greenhouse does not leave any food sources for insects that emerge in the early spring when inside temperatures rise but annual crops are not yet present.
Crop rotation is a valuable cultural management technique for both insects and diseases, and to some extent, weeds. Start your rotation right after a crop is done in the fall by rotating into a cover crop. A winter cover crop does more than just prevent soil erosion; it can help suppress the growth of winter-annual weeds, and its presence promotes biological activity, which helps speed the decay of disease organisms while enhancing soil health.
Before this growing season becomes a distant memory, be sure to make a map of your fields and the location of your crops, so you can effectively move things around over the next few years. In my observation, crop rotation is one of the weakest areas of management, even among talented, experienced growers. Itís usually a seat-of-the-pants affair. Very few growers have a systematic plan for rotating their crops. Those that do often developed it in response to a serious soil-borne disease like Phytophthora!
When planning your rotations, keep in mind that the distance between this yearís and next yearís location of the same crop can have a strong effect on how much insect control you get. While further away is better, even a short rotation distance will help in most cases compared to going back in a field with the same crop. Of course, that only applies to pests that overwinter, like Colorado potato beetle and European corn borer. Pests that fly in from afar wonít be affected by rotation.
When rotating for diseases, especially soil-borne diseases, greater distances between fields from year to year can help, too, by lessening the movement of spores via wind and water. It will be your job to limit the movement of soil and spores via machinery when preparing fields in the spring. Consider power-washing equipment in-between its use in well-separated fields.
While winter cover crops are important for soil management, they arenít without a down side. If you are going to plant into cover-cropped field in the early spring, get the cover crop residue incorporated about a month prior to planting to reduce problems from seedcorn maggots. The adult of this pest prefers to lay its eggs in areas with high organic matter, and rotting vegetation in a freshly tilled field will be more attractive to the flies.
In addition to making a map of your fields and crops for rotation planning, itís also a good idea to do some fall field scouting and make a weed map. A quick scouting can help locate and identify weed problems that may become expensive if they get out of control, and it can provide information that will help you design a weed management program for next year.
Sometime this fall, walk through all your fields and note the following information: How much weed pressure is there now, and was the pressure earlier this year? As you look over a whole field, note the location of weeds. High populations of weeds in the crop rows may be an indication that cultivation equipment needs adjustment, or cultivation needs to be done earlier or more frequently. What species of weeds are present Ė if you cannot identify them take samples or digital pictures and send them to an Extension specialist. Identifying weeds is key to designing a management strategy based on how they grow and when in their life cycles they are most vulnerable.
Weeds like yellow nutsedge, hedge bindweed, and quackgrass are spreading perennials, which have underground parts that can spread throughout whole fields. Because these weeds can be very damaging, and are difficult to control, they are worth nipping in the bud with aggressive and timely cultivation. The best time to control perennial weeds is in the fall. All perennial weeds have storage structures (tap roots or rhizomes) below ground that enable these plants to survive winter and regenerate the following year. Fall tillage of perennial weeds will kill top growth, which stops the production of winter Ďfoodí by photosynthesis, and fragments the storage organs, weakening the plant. It may not kill the weed, so frequent tillage for a period of time may be required to destroy regrowth and prevent re-establishment.
In addition to perennials, keep an eye out for annual weeds that are new to a field or are suddenly increasing in numbers. Some annual weeds can be very difficult to control if allowed to gain a foothold. Hairy galinsoga, for example, thrives under cultivated conditions, and can become widespread on a vegetable farm rather quickly after arriving. Identifying it early and working to eradicate it while you still can, using hand-removal if necessary, is key to saving headaches down the road. 8/04
RETURN TO VERMONT VEGETABLE AND BERRY PAGE