Kentucky Soybeans: Diseases To Be Watching For

Signs of soybean leaves with interveinal chlorosis and interveinal necrosis have been noticed in a number of fields throughout Kentucky not too long ago. Interveinal chlorosis/necrosis is when the leaf tissue between the principle leaf veins turns chlorotic (yellow) or necrotic (brown/useless), however the principle veins stay inexperienced (Determine 1).

Determine 1. Interveinal chlorosis and necrosis signs of soybean leaves (Photograph: Carl Bradley, UK).

There are just a few illnesses or problems that may trigger these signs. Under are descriptions of attainable causes.

Sudden dying syndrome (SDS), brought on by the fungus Fusarium virguliforme is mostly noticed at some degree yearly in Kentucky. Though signs are noticed on the leaves, the SDS fungus truly infects by way of roots and by no means makes it to above-ground plant components. The leaf signs are brought on by a toxin produced by the fungus that strikes up by way of the plant and accumulates within the leaves.

When break up open, the center of the taproot might seem discolored grey to brown when vegetation are affected by SDS. On a considerably uncommon event, plenty of F. virguliforme spores with a blue tint seen to the bare eye could also be current on roots of vegetation affected by SDS.

Administration of SDS happens previous to planting by selecting probably the most resistant varieties out there. Two fungicide seed therapies with confirmed efficacy in opposition to SDS additionally might help with administration of this illness (ILEVO from BASF and SALTRO from Syngenta).

Fields with excessive populations of soybean cyst nematode could also be at better threat of extreme SDS signs, and fields planted early within the season in cool soil temperatures additionally could also be at best threat of an infection and extreme SDS signs.

Determine 2. Darkish lesions on a soybean stem brought on by southern stem canker (Photograph: Carl Bradley, UK)

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Southern stem canker, brought on by the fungus Diaporthe aspalathi, is also often noticed on soybean in Kentucky, particularly when prone varieties are planted in fields which have been steady soybean (non-rotated). Along with the interveinal chlorosis/necrosis signs on the leaves, vegetation affected by southern stem canker additionally may have dark-colored lesions on the stem that may start on the nodes and can unfold throughout the stem (Determine 2).

Administration of southern stem canker begins with planting probably the most resistant varieties out there and rotating to non-host crops (i.e. corn, grain sorghum, wheat). Outcomes from College of Kentucky area analysis trials haven’t proven any impact of foliar fungicides on this illness.

Determine 3. Purple discoloration of decrease soybean stems brought on by purple crown rot and purple spherical fungal buildings often called perithecia produced by the purple crown rot fungus (Photograph: Carl Bradley, UK).

Purple crown rot, brought on by the fungus Calonectria ilicicola, is a brand new illness to Kentucky that was discovered for the primary time within the state in 2021 in just a few fields in Graves County. Along with interveinal chlorosis/necrosis signs on the leaves, the decrease stem and root space across the soil line may have a purple discoloration. Small, red-colored spherical fungal buildings often called perithecia additionally will finally kind on the decrease stem and roots (Determine 3).

Rotating to non-host crops (i.e. corn, grain sorghum, wheat) is a vital step in managing this illness. If discovered, it is very important contact your native county Extension agent to help with getting an correct prognosis and to assist present details about the distribution of this new illness within the state.

Determine 4. Interveinal chlorosis and necrosis of soybean leaves and browning of piths of soybean stems brought on by brown stem rot (Photograph by A. Sisson, Iowa State College).

Brown stem rot, brought on by the fungus Cadophora gregata, is a illness not more likely to happen on a frequent foundation in Kentucky. This illness usually is present in states additional north than Kentucky. To get rid of brown stem rot as the reason for the signs, stems could be break up open with a knife to search for brown discoloration of the pith (Determine 4).

Interveinal chlorosis/necrosis signs additionally could be brought on by phytotoxicity from fungicide merchandise that comprise both prothioconazole or tebuconazole. These signs usually tend to seem when fungicides are sprayed when temperature are sizzling. On this case, signs will solely seem on leaves that have been sprayed with the fungicide, and signs is not going to unfold to new leaves.