Battle for the Belt: Season 2 Episode 13 - Spider Mites

Additional author - Chris DiFonzo, Michigan State University.

Episode 13 of Battle for the Belt is now available: https://www.youtube.com/watch?v=_XL7sqUhZUA

In Episode 13, we have the field crops entomologist from Michigan State University, Dr. Chris DiFonzo, discuss spider mite scouting and management during dry conditions. Luckily, most of the state received rainfall over the weekend giving some relief to crops.

In Ohio, we started with a wet spring, which can bring about slug damage; however, the state is turning toward a hot and dry period which brings different pests to deal with. If we have a long-term dry spell, spider mites (Figure 1) can become an issue.

Spider mites are always around, in ditch banks and roadsides. Spider mites like hot and dry weather, so when those conditions occur, the mites will move into the field from the roadsides into the edges of fields, and depending on how severe the conditions are, they can move further into the field. Generally, spider mite damage can be identified by yellowing field edges (Figure 2).

Spider mites may be found in fields near dirt roads, where the dust can settle on the leaf surface and dry it out. The mites want the leaves dry to lay their webs and become like a “highway” for the insect. Naturally, there is an entomopathogenic fungus, which would normally stop this type of infestation in wetter conditions. However, in the dry areas, infestations can begin.

If you are beginning to have dry conditions and are scouting for spider mites, start scouting the areas that tend to dry out first (e.g., field edges, hilltops, and sandy knolls). There are no economic thresholds for scouting spider mites but there is a visual guide for both corn and soybeans, which can assist in the scouting process (Figures 3 & 4).

For management, an issue with adding an insecticide to the tank for application is that some insecticides will kill off beneficial predatory insects that will prey on spider mites, so in dry situations, that allows spider mites to flourish.

Once you start spraying mites, you only have one chance because you will likely not get all of them and then their eggs survive. Some insecticides kill eggs but are very expensive. If you need to spray spider mites, getting full coverage and using the right product is essential for efficacy.

Scouting to assist in deciding whether it is worth it to spray always pays because there are beneficial insects, that will naturally kill off spider mites. If you are going to spend the money, spend money where it counts.

Many materials for spider mites and insects in field crops are available for scouting, chemical applications, and management. For scouting, identification, and rating there are factsheets for both corn and soybeans, Rating Infestations of Spider Mite on Corn, Rating Infestations of Spider Mite in Soybean, and Twospotted Spider Mite on Soybean. For chemical applications use Field Crops Insect Pest Management Guide and Cheat Sheet for Spider Mite Spraying in Michigan Field Crops.

What’s happening in the field?

This week at the Western location, the date five was planted (Table 1), which means planting 2024 at this location is finished. Soybean planting dates one and two were scouted for Septoria brown spot. Interestingly, planting date one had very low levels while planting date two had almost 80 percent incidence (meaning that most plants presented symptoms at any level, low, medium, or high).

At the Northwest location, date four was planted (Table 1). At this location, the crop growth slowed and only increased by one stage because of the very hot conditions and lack of rain most of this month.

At the Wooster location, date five was planted (Table 1). The crops also stalled in growth and increased by one stage only (also hot and dry weather for the past week). Both planting dates one and two in the soybeans had a high incidence of Septoria brown spots in the lower canopy. Planting date one in the soybeans began flowering.

The soybeans at these locations have been quite short and are not even to 50% canopy closure in the early planting dates (April/early May). The summary of planting dates and conditions from June 17 to June 23 at all three locations is presented in Table 2.

References

DiFonzo, Chris. (2016). Cheat Sheet for Spider Mite Spraying in Michigan field crops. Michigan State University, East Lansing. 46-Miticide-list-for-field-crops.pdf (msu.edu)

DiFonzo, Chris, Tilmon, Kelley. (2021). Field Crops Insect Pest Management Guide. Michigan State University, and The Ohio State University. 2021 IPM Guide Online Version.pdf (osu.edu)

DiFonzo, Chris. (2016). Rating Infestations of Spider Mite on Corn. Michigan State University, East Lansing. 44-MiteScoutingCorn.pdf (msu.edu)

DiFonzo, Chris. (2016). Rating Infestations of Spider Mite on Corn. Michigan State University, East Lansing. 16MiteScoutingSoy.pdf (msu.edu)

Hammond, Ronald, Michel, Andy, Eisley, James. (2014). Twospotted Spider Mite on Soybean. Ohio State University Extension. Twospotted Spider Mite on Soybean | Ohioline (osu.edu)