Top Crop Manager

Features Fungicides Seed & Chemical
A new twist (tie) on gauging control

Are you getting the control you need from your fungicide?

March 4, 2008  By Top Crop Manager

In the world of agricultural research, scientists work diligently to find ways to help potato growers improve their production practices. Computer models have been developed to determine if a crop has enough moisture or if conditions are right to encourage late blight infestation. But, sometimes, a very simple test can be conducted to prove something as basic as how often to spray protectant fungicide.

Dr. Tracy Shinners-Carnelley, a potato pest specialist with Manitoba Agriculture, Food and Rural Initiatives, used a simple twist tie to demonstrate the importance of planning spray
intervals. While she intended to illustrate how to gauge the level of control and when to plan your next application, the demonstration gave her an opportunity to delve deeper into the importance of managing a grower’s pest control strategy for optimum effectiveness.

“We are always trying to prevent late blight and all of the available products work best if applied prior to the disease appearing on the plant,” Shinners-Carnelley explains. “These products protect the plant, but they are contact only so new growth will not have the protection. This is why growers need to carefully plan their application to get good coverage of the plant while it is growing.”

New growth after a spray application will not be protected.

Which is why Shinners-Carnelley took the twist tie off a loaf of bread and attached it to the  newest leaf on the plant and left it for seven days. After a week, she checked the twist tie to see how much growth had occurred. She points out that none of that new growth will have protection from disease. When plants are healthy and the conditions are good, the plants will grow considerably and growers may need to consider that when planning their fungicide applications.

“It’s best to plan your fungicide application based on how much the crop has grown and the environmental conditions, since these factors affect disease risk,” continues Shinners-Carnelley. “Some of the protectant products are labelled for reapplication every five days and some are for seven days, so plan your applications accordingly.” She adds that, if disease pressure is low late in the season and growth has slowed, the period between applications could be spread out.

It is important to develop a plan to get the best coverage of the plant and maintaining appropriate spray intervals, continues Shinners-Carnelley. “Don’t leave long periods where there is no protection,” she cautions. “Always keep disease risk in mind, but make informed decisions. If disease risk is high, you may have to shorten the interval between spray applications. If risk is low, then you can spread out the intervals.”

Risk assessment is key, according to Shinners-Carnelley. Using the twist tie test will give growers an indication of how frequently their spray intervals need to be when compared to the conditions. Perhaps weather conditions have slowed the growth of the plants and the interval can be extended or maybe there has been a growth spurt because weather conditions are great. In one case, a longer interval may be acceptable, but in the other, it may be necessary to switch to a product that allows for a shorter time between re-application.
Compare the plant’s growth with the conditions to determine if the time is right for blight infection and making an informed decision on whether to add more protection to the plant. Too many applications can be costly, particularly if they are unnecessary.

Shinners-Carnelley wants growers to assess their disease pressure, plant growth and environmental pressures before taking the sprayer into the field. She says it is important to plan a strategy, but be willing to adjust it if circumstances change. All this planning could begin with a twist tie and enabling growers to take on late blight with a plan of attack that will protect the crop and preserve yield potential. -end-


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