This week some of the first late leaf spot lesions have been observed on-farm where fungicide applications have been timely at 45 and 60 DAP. This was a few lesions in a limited area and not widespread across the field. Along these lines, this could be the result of variation in spray coverage or penetration into the canopy rather than loss of efficacy of an individual fungicide per se. In either event, this reinforces the value of scouting to see what is going on in each field, as well as product rotation within spray programs.
Pictures are included showing LLS lesions on Emery that were planted this year in a field where infected peanut debris was spread in the fall of 2020, similar to a poor rotation situation. In the first picture, the lesion can be seen near the bottom of the canopy, which could remain hidden if we don’t bend the plants back to peer into the shadows and leaves that lurk beneath. Additional pictures are included comparing a few canopies with regards to 50% laterals touching for growth regulator application.
Also included are trial summary results from 2020 where we looked at fungicide treatment applications after leaf spot had already started in a field. This attempts to compare products for both curative and protectant activity in a relatively uphill situation. For context, the test had between 2 and 6% of the leaves with at least one lesion by 87 DAP (August 21). The test was inverted 45 days later at 132 DAP (October 5). Since this was just one year of data, it is more of an indication of relative product performance under these circumstances rather than unchanging and irrefutable guarantees of performance for all years and locations or environments. A grain of salt.