by Bill and Mary Weaver
Large operations can hire scouts, often Certified Crop Advisors, to alert them to disease and insect problems. Smaller growers can save both crop damage and spray dollars by designating someone to learn to perform the same job.
A scout can save you dollars by telling you whether an economic threshold for disease, insect numbers or insect damage has been reached or whether it’s safe to hold off a spray. How to determine “Economic Thresholds” or “Action Thresholds” is explained in the university-compiled Pest Control Guide for your region, usually available online. A careful scout can also tell you whether a natural predator population is building which can give some measure of control.
Arm your designated scout with an insect sweep net, which can provide a quick census of the insects present in a field and their relative numbers. Also provide a 10x magnifying glass for finding and identifying tiny pests like mites, as well as spotting fungal sporulation in lesions; pocket-sized insect ID and disease symptom guides with photos; a pocket knife for cutting into roots or stems to look for vascular discoloration; access to your region’s university Pest Control Guide, including details on chemical controls and economic thresholds; the funds to send questionable samples to a diagnostic lab for a positive ID; and some paid study time during the off-season to become better acquainted with disease organisms and the life cycles of pest insects in your area.
Use an IPM approach to pest and disease and control, based on the results of regular scouting. This can help you to make informed management decisions, giving you the best control at the lowest cost. IPM provides several categories of management tools.
First check out possible cultural tools. Irrigation that wets both crop leaves and row middles disrupts mating and egg laying in mites. Other important cultural tools include fall tilling of crop residue where pests and disease could overwinter. If the crop residue decomposes, they will be unable to survive. If your scout finds root rots or fungal lesions associated with waterlogged soil, plan to prevent these problems in next year’s crop by creating better drainage in that section of the field. Crop rotation is another important cultural tool to cut populations of specific disease and pest organisms. Preparing raised beds is a cultural tool that can help to prevent phytophthora blight in squash and peppers, for example. Spacing plants farther apart to allow for better air circulation can help to prevent many fungal diseases. Use of reflective mulch will confuse aphids from feeding on plants where they could inject disease-causing viruses. Using cultural tools can prevent the need for many chemical applications.
Use forecasting tools available from your university. Watch degree-days and day length to catch the first emergence and onset of overwintering pests. Follow temperature and humidity forecasting systems designed to predict likelihood of particular diseases like late blight. MELCAST is a weather-based disease forecasting program for melons and cucumbers. The National Cucurbit Downy Mildew Forecasting can alert you when outbreaks of downy mildew occur in your area. Your University may also make available the results of black light catches of night flying moths, which predict upcoming problems with “worms” in corn and cabbage-family plants.
To prevent specific disease and insect problems next year, plan to use resistant/tolerant varieties whenever possible.
Finally, when using chemical controls, use the most selective pesticides that will accomplish the job. Prevent the build-up of pesticide resistance by rotating different modes of action, noting FRAC and IRAC codes. Re-entry times for workers and days-to-harvest must fit your needs. Note also the maximum number of times a given pesticide can be used per season. Chemical choices often involve a complex juggling among the many priorities important to a grower.
Learn from your experiences. Ask your designated scout to keep detailed records of the first sightings of problem insects and of specific diseases. Be sure to keep records of chemical controls tried and of their effectiveness.
Ann Harrison, Technical Services Rep for BASF and a licensed PCO adviser, fleshed out how some of these IPM approaches should be used in a recent webinar from GenNext. Her principles are instructive and worthwhile.
First, use the right scouting method. If you’re checking for the presence of root-damaging nematodes, for example, take your sample from at least six inches deep. In scouting for insects and diseases, it’s important to check the undersides of leaves, the growing point(s), the stem, where the stem enters the ground and any fruit. “You can check a whole field, but if you give a cursory look, or check the wrong places, you’ll miss important information.”
Ask your diagnostic lab how to package samples for shipping. As a general rule, refrigerate samples immediately and plan to ship by overnight mail in crush-proof packaging. Dig roots for diagnosis with soil attached to the root ball. “You want leaf samples showing symptoms, but that contain live tissue,” Harrison emphasized. “Include with each sample the past disease history of the field.”
If there is a pattern to the damage, you could be dealing with herbicide damage rather than disease. “For example, if the plant or leaf damage is found only at the ends of the rows” the herbicide spray operator may have left the sprayer nozzles on during turns. Certain types of damage can also suggest herbicide drift from another field, such as shepherd’s hooking in plant tips.
Nutritional deficiencies can masquerade as diseases. Obtaining a correct diagnosis at a lab can save unnecessary sprays.
Also, notice the condition of the soil, Harrison continued. “If the soil appears waterlogged, from over-irrigation for example, your problem could be a root rot or a lesion that may contain fungal sporulation.” In the latter case, send a branch with a lesion for diagnosis.
Check throughout the field, not just the edges. With some pests and diseases, it may be effective to treat only specific areas if the damage is confined to a portion of the field or orchard.
Contact sprays, even if combined with a good spreader/sticker, do not, in most cases, have residual activity. However, check with your dealer when you purchase them. A few contact sprays do. The majority of contact sprays will not protect new growth unless resprayed.
Systemic sprays, on the other hand, move through the vascular system, can protect some new growth and may provide some curative action. Be aware of the weather forecast for the week or two following when you’re considering spraying a systemic, however, cautioned Harrison. If a spell of cool, overcast weather would follow your application of a systemic through drip irrigation, for example, not enough chemical may be translocated to the foliage to provide protection, even though applied correctly and following label directions.
If upcoming weather looks unpromising for translocation of a systemic, noted Harrison, use a foliar application of another chemical instead. Scouting in the real world requires an awareness of many factors.