Manganese deficient onions take on a yellowish green color and the leaves also droop as if moisture stressed. Chelates of Mn can also be used, but be sure to follow the labeled rate, because with some materials applying more than 0.5 to 1.0 lb Mn per acre can cause some burn on the foliage. When diagnosing Mn deficiency, you should check the soil pH, nitrogen status, and foliar signs of the crop. Excess nitrogen in the soil can stimulate excess vegetative growth, delay fruit development or crop maturity, and reduce vegetable quality. Consider applying lesser amounts to the foliage.
Leaves can readily absorb nitrogen in the nitrate, ammonium, or urea form.
When there is a perceived need for additional nitrogen during the latter stages of vegetable crop development, confirm this with a petiole sap or leaf tissue nitrogen test. For some crops, it may be desirable to reduce the amount of topdress nitrogen in favor of foliar N application. With a good foliage canopy, the efficiency of nitrogen use is higher from nitrogen applied to the foliage than to the soil. A large upper air ridging pattern currently across the western U.S. is forecast to slowly move eastward towards the Great Lakes by early next week. As this ridge approaches, temperatures will slowly increase to above normal levels continuing through much of next week.