If the crop is adequately protected, there comes a point when there is not enough time left in the season for diseases to cause significant damage. That said, there is still enough time until harvest that things could go south in a hurry if growers are not careful.
By now, most growers will have begun to see light at the end of the tunnel for this year’s cropping season. Corn has been picked or will be shortly. Peanuts and cotton are entering the 4th quarter as the end of their game nears.
In these times I am often asked to make late-season disease management recommendations. While recommendations may vary from state to state, I tell growers you must remain vigilant against peanut leaf spot and southern stem rot (white mold). You should be aware of target spot through about the sixth week of bloom and areolate mildew until four weeks from defoliating the cotton. Our soybean producers should consider protecting their crop until the R6, full-seed, growth stage from Asian soybean rust and Cercospora leaf blight.
Too Much Disease?
Recommendations for crops that are free, or nearly free, from disease going into the 4th quarter are usually easy for me to make. My advice for growers in such situations is to stay the course, keep on an appropriate schedule. Recommendations are also straight-forward when there is too much disease in a field. Too much is characterized by widespread foliar disease (leaf spots, rusts, mildews) affecting most of the field and where significant defoliation has already occurred.
Too much also occurs in fields where white mold has experienced a jail break and runs up and down the rows with impunity. Where disease has advanced in a field to a level where any additional use of fungicides is fruitless, then recommendations are straight-forward as well. Unless the grower simply must do something to feel better, there is likely nothing that can be done to reverse or slow the damage that has occurred and will continue to occur.
Because growers invest heavily in fungicides, they have a right to high expectations for performance. High expectation is a good thing, but unrealistic expectation is not. For example, no fungicide program can completely exclude white mold from a peanut field nor exclude every spot on a leaf. At their best, fungicides can inhibit the spread of disease from an initial infection to affecting many plants in the field. While I am impressed at fields that are very nearly disease free, I also wonder at what cost.
Where the level of disease in a field is appropriate given that it is simply part of growing a crop, there is no need to change anything. Often, even the perception of a problem in a field may cause growers to change fungicides. When faced with such, despite my assurances that there is nothing better than what they are already doing, I will offer alternatives that are similar in efficacy.
Where disease really is developing later in the season, for whatever reason, my recommendations are to:
- Tighten the spray interval.
- Insure adequate coverage.
- Consider switching to a more effective product with increased curative activity.
- Remember fungicide resistance.
While there is little hope of reversing damage that has already occurred, adopting such strategies could help to reduce further losses.
Making effective recommendations is challenging and requires both science and art. Sometimes there are no obvious solutions to a problem, nor a single best answer. Recommendations offered to farmers in Georgia may be different than recommendations made in other southern states. Reasons for this include differing production practices, a differing disease spectrum and threat from diseases based upon environmental conditions, and simply our differences in experience and perception.
Because they are aggressive in use of fungicides on peanut, growers in Georgia are prepared to be more aggressive with use of fungicides on other crops as well, when the need and opportunity for profit are there. The key to every recommendation is that it will increase profit for the grower at harvest. Late in the season, a best recommendation may urge the grower to take swift and immediate actions to slow disease. In other situations, the best recommendation may be to stand down and do nothing but learn for next season.