Bobbi Stevenson-McDermott August 16, 2015
The sights and sounds of Yuma County agriculture in August! Looking at the fields there is a lot more brown than green at this time of year. Growers are in the midst of harvesting Sudan hay, Sudan seed, dried beans and peas, alfalfa hay, Bermuda grass hay and seed and other specialty seed crops. Cotton growers will probably start early picking in late August. The weather has been tough with all the extreme heat and humidity. Wheat fields have been harvested, stalks baled and the remaining organic matter turned into the soil.
Now is the time that the heavy tillage is done, while the soil profile to a depth of 3 feet or more is very dry and rippers can break up compacted layers and facilitate the soil structure. The soil structure determines how much air and water will get to the root zones of the coming produce crops.
This year, there seem to be many fields being bedded and then the beds covered with sheets of plastic. This process is called solarization, a method of weed control. The heat builds up under the plastic to temperatures which will kill many weed seeds, reducing the need to use tillage and herbicides later in the year. There solarization may also help with insect and disease problems.
Along Highway 95, there are fields which are being continuously flooded for days at a time. The practice of keeping a field saturated with water is thought to help to control the lettuce disease Sclerotinia sclerotiorum. The sclerotia, or the fungal ‘seed’, become hard and black when they mature. The sclerotia act like seeds and allow the fungus to survive for several years in the soil. Control of Sclerotinia diseases must be accomplished by using a combination of cultural and chemical means. Presently, resistant lettuce varieties have not been successfully developed with enough resistance to make this a feasible means of control. Activity of this pathogen favors high soil moisture, high air humidity and cool temperatures. Research has shown that the use of drip irrigation can dramatically reduce both factors near the soil surface and reduce the incidence of Sclerotinia diseases. Crop rotation is another important tool in reducing the disease population in the soil. Planting non-host crops as corn, small grains and grasses are suggested rotation crops.
It should be mentioned that a non-crop fallow period does little to reduce the disease population. The wetting and drying of soil that occurs during a cropping cycle is much more effective in reducing the number of active sclerotia in the soil. Deep plowing has been recommended to help reduce Sclerotinia diseases, but recent research does not support this practice. There are a number of fungicides that have excellent activity against Sclerotinia.
Avoiding overly wet soils by keeping the lettuce bed surface as dry as possible with careful irrigation is important as is irrigation water management and good soil drainage.
There are continual improvements to the technology used in the produce industry. One of the newest is a plant tape. Most folks understand what a seed tape is, some type of material with seeds imbedded in it that is merely planted, watered and then the seed grows. One of the problems with planting vegetable seed is that it is extremely expensive, from hundreds to thousands of dollars per pound. While everyone uses precision seeders, most crops grown from seed must be thinned so the heads develop uniformly. While mechanical thinners were demonstrated at the Yuma Ag Summit in February, 2015, the technology still is in the development stage. Also with the planting of seed, there is a percentage of the seed that do not germinate, leaving gaps in the crop line, something no grower wants to see. A U-Tube video I recently saw shows little germinated lettuce on a tape. A machine then installs the tape with the plants on the field rows. Plants are spaced on the tape at the optimum distance for head development. If this technology becomes commercially successful it will greatly reduce the labor needed early in the crops growing season.
In a visit last year to a transplant growing facility, I was surprised to learn that some growers are already transplanting some lettuces. In addition, watermelons, cantaloupes, herbs and many other crops are being transplanted because a viable plant is going into the field.
All these changes in the early stages of produce production may in the long run reduce the production costs for these crops. Yuma County growers continue to be leaders in the development of more efficient and environmentally sound methods of growing produce, worthy of the Winter Produce Capital!
Bobbi Stevenson-McDermott is a soil and water conservationist. She can be reached at firstname.lastname@example.org.