With the corn advancing rapidly in the presence of extreme heat and humidity we have to sit back and think what kind of yield impact are we going to recognize from the lack of moisture. As the dry weather continues through out Essex, Kent, Lambton and Middlesex counties more and more corn fields are showing signs of moisture stress with leafs rolling and stalks starting to fire up. In some fields soil moisture is available but just out of reach of the corn roots.

Fields that seem to be weathering the dry weather the best are the ones sidedress with Anhydrous followed by sidedressed 28%, then Urea preplant incorporate, followed last is 28% preplant incorporate.

Yield impact can be directly related to the number of days the crop shows stress during the different growth stages. The following summarizes the findings of Iowa research by Claassen and Shaw on effects of drought on grain yields in corn.

Vegetative Stages

Claassen and Shaw’s findings were that four days of stress (corn wilted for four consecutive days) at the 12-14 leaf stage has the potential of reducing yields by 5-10%. Kernel rows are determined by the 12th collared leaf stage and the potential number of kernels per row is complete about one week before silking.

Tassel Emergence

As the tip of the tassel begins to emerge from the whorl, the upper stalk internodes rapidly elongate and the ears begin to expand. Silks from the base of the ears are also elongating. Four days if moisture stress at this stage has the potential to reduce yields 10-25%.

At this stage leaves and tassels are fully emerged and the cobs and silks are growing rapidly. This is the most critical period in terms of moisture stress at this stage has the potential to reduce yields by 40-50%.

Blister Through Dent

12- 36 days after silking, the cobs, husks and shanks are fully developed and the kernels are increasing in dry weight. Moisture stress will reduce kernel fill from the ear tip down. Four days of drought at the blister stage has the potential of reducing yields by 30-40% and at the dough stage by 20-30%.

Through out the year (present and past) your local crop specialist has been keeping visual and written notes on the performance of Mycogen, Dekalb and N.K hybrids on how they adapt to the various soil types and weather conditions through out southwestern Ontario. Please feel free to contact your local rep and they can aid you in choosing a variety that’s right for your farm. Hope to see some of you out at the Stoney Point Crop Technology Day, Friday August 23rd.

Ray Simard