Western bean cutworm update and tips for post wheat harvest manure application for Ontario producers

OMAFRA Field Crop Team
August 11, 2017
By OMAFRA Field Crop Team
Western bean cutworm (WBC) continues to be a concern for pollinating corn in areas with high trap counts. Peak moth flight has occurred in counties in the southwest but counties in Central and Eastern Ontario have not reached peak yet. Moths will now be looking for late planted corn that is still in the early tasseling stages or will focus on edible beans. Focus scouting efforts in those corn fields that do not have dried silks yet. Edible bean growers need to scout for pod feeding once pods are present. Edible bean fields that are adjacent to corn fields that reached WBC eggmass threshold this year are likely also at risk. It is best to control fields as soon as pod feeding is observed. The larvae are exposed to the insecticide when they make holes in the pods to get to the seed. For additional information on WBC thresholds as well as optimal scouting and insecticide application timing, click here. Information on product choices is available in the OMAFRA Field Crop Protection Guide.

Post Wheat Harvest Manure Application
For livestock producers and those using organic amendments, the post wheat harvest season is an excellent opportunity to apply manure for nutrients and organic matter. Spreading workload, reduced compaction and reduced risk of environmental losses from runoff and erosion, as well as the opportunity to combine the benefits of feeding cover crops with manure, are all benefits of manure applied during the growing season.

Where manure or other organic amendments are applied to fields it is important to take a sample for analysis to help determine available nutrients and potential commercial fertilizer savings. Along with analysis for N, P and K in manure, additional tests will help determine nutrient availability. Testing for sulphur will provide an indication of elemental sulphur content which is released to a crop similar to organic nitrogen and can provide all or some of the sulphur needs, especially for wheat and forage crops. Testing for C:N (carbon to nitrogen) ratio for solid manure and amendments will help indicate if additional commercial N will be required for a corn crop. C:N ratios below 20:1 will have adequate nitrogen to help with the breakdown of carbon. Materials with C:N ratios over 30:1 (especially for spring applied materials) should determine with pre-side dress N test if addition N will be required. With liquid materials, testing the pH will help determine the potential for rapid ammonium N loss where manure is not injected or immediately incorporated. Liquid manure with high NH4-N levels combined with high pH (above 7.8) will lose the majority of the quickly available nitrogen in the first 24 hours, especially when combined with warm dry soils and/or high winds over bare soils.

Often there is too little credit given to the nitrogen supplied by fall-applied manure. A general guideline with fall applied manure is to credit half the total nitrogen from the analysis. Cattle manure with heavy bedding and/or amendments with high carbon to nitrogen (C:N) ratio will have lower (30 to 40 per cent) nitrogen credit while broiler poultry manure will have higher N credits (50 – 60 per cent). Mild winter conditions will increase available N from solid manure but can reduce nitrogen contribution from liquid manure where ammonium N (NH4-N) is higher. An early warm period in spring also increases nitrogen contribution from manure to a crop, while a cool wet spring will slow down nutrient release; not able to meet the N needs of a rapid growing corn crop during the period ahead of pollination. Slow release nitrogen from manure will contribute to yield after pollination, especially in areas where frequent and heavy rain may have resulted in denitrification or leaching of commercial N sources. Tissue tests of fields with evidence of some N deficiency on lower corn leaves reveal that levels are still within the normal range. Where manure or other amendments were applied there should be adequate nitrogen to meet remaining crop needs.

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