Soybeans Aphids Persist But No Panic – OMAF

Soybeans Aphids Persist But No Panic – OMAF

on August 26 | in Ag News | by | with No Comments

From OMAF Field Crop Report

Soybeans: Gilles Quesnel

Most soybean fields are at the R5 stage (seeds are 3 mm long in the pod at one of the four upper nodes on the main stem). Soil moisture is generally adequate for seed fill and across the province pod set ranges from average to excellent.

Two-spotted spider mites are starting to show-up in drier areas. Mites feed on individual plant cells on the underside of leaves where each feeding site causes a stipple/dot. Severe stippling causes yellowing, curling and bronzing of the leaves and the damage is more severe in hot, dry weather. Spider mite infestations usually start at the edges of fields with pockets moving deeper into the field. From the road, these pockets may be confused with drought stress. High-risk factors include neighboring winter wheat stubble, hay fields, mowed grass and ditch banks. Rain along with cooler weather will reduce numbers in fields naturally to below the threshold necessitating control measures. Fields should be sprayed if they are above this threshold which is one damaged leaf per plant up to the R6 growth stage (seeds within one pod on the top four nodes fills the pod cavity). Dimethoate is the only registered product that will control spider mites in soybeans.

Soybean aphids can still be found across much of Ontario and population has jumped in a few areas. Fields should still be monitored until plants have reached the R6 (full seed) growth stage, which should occur the end of August/early September. White mould is present in some fields, but infection levels are mostly lower than anticipated considering the frequent precipitation in June/July, likely due to the low inoculum levels of the last few years which experienced hot dry summers.

 

Forages: Joel Bagg

While it is tempting to cut alfalfa in the fall, the decision should weigh the immediate need for forage against the increased risk of alfalfa winterkill and reduced yields next spring. The Critical Fall Harvest Period for alfalfa is the 6-week period preceeding the average date of a killing frost. Not cutting during this rest period a