Spidermites

Amy Timmerman, Extension Educator Author

11/17/2022 Added

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We are starting to get more reports of spider mites damaging corn and soybeans in Nebraska. Two species of spider mites, the Banks grass mite and the twospotted spider mite, commonly feed on Nebraska corn.

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[00:00:00.776]This is Amy Timmerman with this week’s extension update.
[00:00:03.626]We are starting to get more reports of spider mites damaging
[00:00:06.646]corn and soybeans in Nebraska.
[00:00:08.876]Two species of spider mites, the Banks grass mite and
[00:00:12.476]the twospotted spider mite, commonly feed on Nebraska corn.
[00:00:15.766]Banks grass mites feed almost exclusively on
[00:00:19.445]grasses, including corn, small grains and sorghum.
[00:00:22.855]Twospotted spider mites not only feed on many species of grasses, but also
[00:00:26.575]on soybeans, fruit trees and a variety of vegetables and ornamental plants.
[00:00:30.575]The carmine mite is now considered the same species as the twospotted spider mite.
[00:00:35.195]This spider mite species is a distinctive dark red color,
[00:00:38.895]but otherwise identical to the Twospotted spider mites.
[00:00:42.417]Although these two species - the Banks grass mite and the twospotted spider mite -
[00:00:46.607]are somewhat similar in appearance, they differ in several biological
[00:00:50.241]characteristics and their susceptibility to pesticides.
[00:00:54.241]Mites damage crops by piercing plant cells
[00:00:58.241]with their mouthparts and sucking the plant juices.
[00:01:00.721]The first evidence of mite feeding - which usually can be seen on the
[00:01:04.021]top of the leaf - is a yellow or whitish spotting of the leaf tissues in areas
[00:01:07.851]where the mites are feeding on the lower leaf surface.
[00:01:10.541]Because many other things can cause similar discoloration, it is important
[00:01:14.021]to check leaves closely to make sure mites are actually causing the damage.
[00:01:18.626]Leaf discoloration caused by mite feeding can be easily identified by checking the
[00:01:23.073]undersurface of leaves for the presence of mites, eggs and webbing.
[00:01:27.601]Both Banks grass mites and Two-spotted spider mites produce webbing,
[00:01:31.501]and a fine network of silken webs likely will be associated with mite colonies.
[00:01:36.242]A magnifying glass or 10X hand lens is a helpful tool in examining plants
[00:01:41.922]for the presence of mites.
[00:01:43.892]Spider mites are very small in size. An adult female are about 0.016 inch in length
[00:01:50.682]and other life stages are even smaller and can be difficult to be seen without a
[00:01:54.682]magnifying glass or 10X hand lens.
[00:01:58.312]As mite infestations develop, leaves may be severely damaged
[00:02:01.812]and the food manufacturing ability of the plant may be progressively reduced.
[00:02:06.039]If an infestation is severe, leaves may be killed.
[00:02:09.799]In corn, effects on yield are most severe when mites start damaging leaves
[00:02:13.319]at or above the ear leaf.
[00:02:16.224]Infestations may reduce corn grain yields due to poor seed fill and
[00:02:19.574]have been associated with accelerated plant dry down in the fall.
[00:02:23.294]The quality and yield of silage corn also may decline due to mite feeding.
[00:02:27.626]Damage is similar on soybeans and includes leaf spotting, leaf droppage,
[00:02:32.160]accelerated senescence and pod shattering, as well as yield loss.
[00:02:37.304]Early and severe mite injury left untreated can completely eliminate yields.
[00:02:42.104]More commonly, mite injury occurring during the late vegetative and
[00:02:46.104]early reproductive growth stages will reduce soybean yields 40%-60%.
[00:02:51.192]Spider mites can cause yield reductions as long as green pods are present.
[00:02:57.095]Mites do not cause severe economic damage every year in Nebraska.
[00:03:01.455]Several factors, which fluctuate from year to year,
[00:03:04.505]strongly influence spider mite numbers.
[00:03:06.705]Probably the most important of these factors are weather, natural enemies and pesticide use.
[00:03:11.346]Overwintering sites that are close to corn and soybean fields,
[00:03:14.773]especially grasses, wheat, and perhaps alfalfa, also may increase
[00:03:18.643]the possibility of mite invasion.
[00:03:21.153]Dry, hot weather favors mite reproduction and survival,
[00:03:24.743]especially if accompanied by drought stress in the crop.
[00:03:28.163]When the weather in June, July and August is especially hot and dry,
[00:03:32.163]mites can reach damaging numbers in most corn and soybean growing areas of Nebraska.
[00:03:36.550]Major mite infestations are more likely to occur in central and western counties
[00:03:40.869]that normally experience less rainfall.
[00:03:43.929]Sandy soil types also may contribute to spider mite problems in these areas
[00:03:47.989]because crops grown on these soils are more likely to experience drought
[00:03:51.549]stress even when irrigated.
[00:03:54.419]Questions regarding managing spider mites please contact your local extension office.
[00:03:59.035]This has been Amy Timmerman with Nebraska Extension.

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Spidermites

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