Many reports are coming in about silk clipping in corn. Three main culprits include corn rootworm beetles, Japanese beetles and redheaded flea beetles. Regardless of which one is doing it, it comes down to when and where they are clipping and by how much. Corn silks can grow as much as an inch or more a day, though most of the rapid growth is in the first few days of pollination and drought stress can slow down this growth. The key is to figure out how much feeding the beetles are doing versus how much silk the plants continue to grow. Three questions to ask: 1. Are the beetles feeding on more silks than the plants can put out? 2. Is it across the field or just closer to the field’s edge? And most importantly, 3. Are the beetles still actively feeding in the field?
Silk clipping thresholds only apply for the first half of the pollination period. After that, the majority of the pollen has already landed on the silks and started fertilization. As long as the silks are approx. 1/2 inch or longer during that period, they can still catch pollen.
Silk clipping is always worse in the rows closest to the field edge but it is important to assess the field as a whole before deciding if spray is necessary. Scout 5 plants in 10 areas of the field. You will need to do this at least twice to determine if the plants are able to grow ahead of the feeding or if the beetles are winning. Scout 1 or 2 days after the first scouting trip to see if the silks have grown. Control is only necessary if silks have been clipped to less than 1/2 inch (1.25 cm) before 50% pollination and the beetles are still actively feeding.
Also look for spider mites and western bean cutworm eggs before making a spray decision. Products used to spray for beetles could flare up spider mite populations and potentially limit your options for spraying WBC eggs if the field hasn’t reached WBC egg threshold yet. A WBC article is on deck for later this week but a quick synopsis is that trap catches are starting to increase but we are not at peak yet. So spraying now for WBC too might be premature if more eggs will be laid in the next few weeks and reach threshold.