There are times when investigating the cause of damage to a crop that there is no one clear answer to the problem, and one is left to theorize based on all of the evidence available. This happens to be one of those cases.
In 2009, I received a call from Ted, who farms 3,700 acres of wheat and canola near Olds, Alta., at the beginning of August. Ted was concerned that the pods on his canola plants, a glyphosate-tolerant variety located in one of his fields, were not forming properly. He thought there may be a problem with the variety because the other varieties of canola he had planted were healthy and normal. To him, the damage in that particular field seemed so extensive he was ready to get a neighbour to silage it.
Upon investigation, I observed the main stems and branch racemes of the canola plants lacked the number of pods a healthy stand would normally produce. The bottom 20 per cent of the raceme had formed small underdeveloped pods, those on the next 55 per cent of the raceme had been aborted and the top 25 per cent had flower buds and was beginning to flower. This abnormality was found uniformly across the entire field. Also, Ted’s crop was much further behind in maturity when compared to neighbouring fields. But the plants did not appear to be damaged in any other way. The only other observation of note was the heavier residual straw in this field when compared to those surrounding it.
In order to rule out variety as the issue at hand, we checked with the producers of neighbouring farms about how their canola stands of the same variety and seed lot were developing. Canola stands of the same variety and seed lot were producing normal healthy stands; variety was not the problem. Also, after investigation, we concluded fertilizer rate, disease, pest pressure, herbicide residue in the soil and tank residue contamination could not be responsible.
But, Ted had sprayed a second application of herbicide at the 10 to 15 per cent flower stage — this was beyond the recommended latest application stage of six leaves. This late application may have stressed the crop during the critical flowering process, which could lead to a decrease (or absence) of pod formation. If this was the case, once the canola plants recovered from this stress they began to flower properly allowing normal pod development to occur, but later in their development.
Also, the end of July presented moderately high temperatures, which may have led to some flower blasting. Because of the residual straw cover, this particular crop may have been behind in development compared to neighbouring crops. The straw would have kept the soil cooler in the spring, leading to slower emergence and development. Thus, the higher temperatures in July would have caught these plants at a vulnerable stage, resulting in flower blasting — and no pod development. After the heat event, temperatures returned to lower levels and the plant recovered and finished flowering. This would explain the interruption in pod development.
Most likely, the delay in maturity, flower blasting and pod abortion in Ted’s canola plants occurred as a result of the combination of these various stresses: slower emergence due to the residual straw, late herbicide application and heat stress.
When things go wrong with respect to plant development, often it is due to several different factors instead of a single one. In this case, I recommended Ted allow the crop to mature because the top of the main stem and branches appeared to be flowering and producing pods properly. As a result, the crop ended up yielding only 30 per cent less than average — although the quality was poor and it was difficult to market. Canola plants are very resilient and Ted’s crop recovered somewhat from the stresses it had undergone.
In the future, I recommended that Ted be very diligent about staying within the herbicide application guidelines. Also, in years of extreme straw production, to remove or uniformly spread the straw to allow for quick and even germination and emergence in the spring. Seeding early will minimize the chance of heat stress during the flowering stage.