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Importance of crop diversity and pest control
Grass is always greener...
Don Gardner is the University of Georgia Extension agent for Bryan County. He lives in South Bryan. - photo by File photo

Last time I briefly discussed the importance of having genetic diversity in our crop plants and the importance of having pesticide diversity.

It is important to understand that controlling a pest does not mean killing every weed or every insect in a field or every fungus spore on a crop plant.

That tactic puts huge pressure on a pest to adapt and change into something that is tolerant or resistant or immune to our control methods. Our objective is to lower the disease incidence or predation by the pest on our crop to a level that does not cause us economic loss.

We try to strengthen the weakest link in the chain. For example, if your cotton combine leaves 10 percent of the lint in the field but uncontrolled stinkbug will cause a 20 percent crop loss, just knock the stinkbug population down to a point it only costs you 2 percent yield loss and spend the money you saved on not making that third stinkbug spray on getting the combine tuned up so it only leaves 5 percent of the lint in the field.

The point being that growers are interested in maximizing yield and income, not killing every bug. Killing every pest bug is actually counter-productive to agricultural production interests.

Pesticides are expensive. The least expensive way for a nation to reduce crop losses due to pests is to breed resistant varieties. I worked on soybean root rot back when I was young, slender, fit and had hair. Crop breeders would backcross genes for resistance to the fungus into soybean varieties but within just a couple years the resistance would break down in the field. My professor decided to have us look at the fungus races in the soil and see how many races of the fungus there were. The breeders knew about 18 races. Our team found over 40 in the soil waiting for us to force them to the forefront with our breeding programs.

A solution to the issue was to bait fields directly from the soil and find out what were the most prevalent races of the fungus and then plant soybean varieties that carried resistance to those races.

Plants could carry resistance to multiple races, but it was not economical to develop a variety with resistance to all races. Instead of trying to breed a Secretariat, we bred a stable of very capable ponies, some good on dry turf and some that thrived on a muddy track. Each planting season the farmer could match the variety he planted to the fungus races they would likely face.

This was not an original idea. We have been managing the cereal rusts of wheat, oat, barley and rye in North America using resistant varieties since the 1950s when these fungus diseases caused losses of as much as 40 percent of the wheat crop.

There are 77 known races of leaf rust, 49 races of stem rust and 43 races of stripe rust that the scientists at the USDA Cereal Disease Lab monitor annually. Every year the varieties if cereal grains planted are changed to respond to changes in the profile of rust races from the previous year. The wheat variety that you eat in your bread this year is not the same one now being grown in the field for next year.

This control of cereal rusts through use of resistant cereal varieties has been very successful for 60 years, but there is a potential threat on the horizon. In Uganda in 1999 a new virulent stem rust race tagged UG99 (for Uganda isolate 1999) was identified. It was virulent to the Sr31 rust resistance gene. This gene was so stable that in 1997 some 80 percent of the wheat planted in Africa, the Indian subcontinent, China, Europe and South America carried this gene. Nothing had ever shown virulence to this gene before.

This new threat with its potential to cause worldwide famine is getting attention. In 2008 the Bill and Melinda Gates Foundation awarded $26.8 million toward stopping this rust. Managing diversity in crops and pests is a secure job. Monitoring for new diseases, testing new pest controls and breeding better-performing plants and livestock is a constant process. Worldwide trade breaks through natural barriers to potential pests. Storms carry insects and fungi long distances allowing ocean barriers to be spanned. Sometimes we help create new threats by putting too much pressure on a pest, forcing it to improvise, adapt and overcome. Some new threat is always making an appearance.

We ignore these threats at our own peril. Most of the battles occur out of the spotlight and without the public taking any notice, but the unnoticed save lives by preventing starvation through increasing crop yields and reducing crop losses.

Next time: The base program is anchored in reality.

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