Spider Mites - August 1, 2022 - Amy Timmerman, Extension Educator
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- [0:00] This is Amy Timmerman with this week’s extension update.
- [0:03] We are starting to get more reports of spider mites damaging
- [0:06] corn and soybeans in Nebraska.
- [0:08] Two species of spider mites, the Banks grass mite and
- [0:12] the twospotted spider mite, commonly feed on Nebraska corn.
- [0:15] Banks grass mites feed almost exclusively on
- [0:19] grasses, including corn, small grains and sorghum.
- [0:22] Twospotted spider mites not only feed on many species of grasses, but also
- [0:26] on soybeans, fruit trees and a variety of vegetables and ornamental plants.
- [0:30] The carmine mite is now considered the same species as the twospotted spider mite.
- [0:35] This spider mite species is a distinctive dark red color,
- [0:38] but otherwise identical to the Twospotted spider mites.
- [0:42] Although these two species - the Banks grass mite and the twospotted spider mite -
- [0:46] are somewhat similar in appearance, they differ in several biological
- [0:50] characteristics and their susceptibility to pesticides.
- [0:54] Mites damage crops by piercing plant cells
- [0:58] with their mouthparts and sucking the plant juices.
- [1:00] The first evidence of mite feeding - which usually can be seen on the
- [1:04] top of the leaf - is a yellow or whitish spotting of the leaf tissues in areas
- [1:07] where the mites are feeding on the lower leaf surface.
- [1:10] Because many other things can cause similar discoloration, it is important
- [1:14] to check leaves closely to make sure mites are actually causing the damage.
- [1:18] Leaf discoloration caused by mite feeding can be easily identified by checking the
- [1:23] undersurface of leaves for the presence of mites, eggs and webbing.
- [1:27] Both Banks grass mites and Two-spotted spider mites produce webbing,
- [1:31] and a fine network of silken webs likely will be associated with mite colonies.
- [1:36] A magnifying glass or 10X hand lens is a helpful tool in examining plants
- [1:41] for the presence of mites.
- [1:43] Spider mites are very small in size. An adult female are about 0.016 inch in length
- [1:50] and other life stages are even smaller and can be difficult to be seen without a
- [1:54] magnifying glass or 10X hand lens.
- [1:58] As mite infestations develop, leaves may be severely damaged
- [2:01] and the food manufacturing ability of the plant may be progressively reduced.
- [2:06] If an infestation is severe, leaves may be killed.
- [2:09] In corn, effects on yield are most severe when mites start damaging leaves
- [2:13] at or above the ear leaf.
- [2:16] Infestations may reduce corn grain yields due to poor seed fill and
- [2:19] have been associated with accelerated plant dry down in the fall.
- [2:23] The quality and yield of silage corn also may decline due to mite feeding.
- [2:27] Damage is similar on soybeans and includes leaf spotting, leaf droppage,
- [2:32] accelerated senescence and pod shattering, as well as yield loss.
- [2:37] Early and severe mite injury left untreated can completely eliminate yields.
- [2:42] More commonly, mite injury occurring during the late vegetative and
- [2:46] early reproductive growth stages will reduce soybean yields 40%-60%.
- [2:51] Spider mites can cause yield reductions as long as green pods are present.
- [2:57] Mites do not cause severe economic damage every year in Nebraska.
- [3:01] Several factors, which fluctuate from year to year,
- [3:04] strongly influence spider mite numbers.
- [3:06] Probably the most important of these factors are weather, natural enemies and pesticide use.
- [3:11] Overwintering sites that are close to corn and soybean fields,
- [3:14] especially grasses, wheat, and perhaps alfalfa, also may increase
- [3:18] the possibility of mite invasion.
- [3:21] Dry, hot weather favors mite reproduction and survival,
- [3:24] especially if accompanied by drought stress in the crop.
- [3:28] When the weather in June, July and August is especially hot and dry,
- [3:32] mites can reach damaging numbers in most corn and soybean growing areas of Nebraska.
- [3:36] Major mite infestations are more likely to occur in central and western counties
- [3:40] that normally experience less rainfall.
- [3:43] Sandy soil types also may contribute to spider mite problems in these areas
- [3:47] because crops grown on these soils are more likely to experience drought
- [3:51] stress even when irrigated.
- [3:54] Questions regarding managing spider mites please contact your local extension office.
- [3:59] This has been Amy Timmerman with Nebraska Extension.