|April 1, 2003
On March 30, cold temperatures covered most of the region and it was low enough to be of concern. Some of the fields I looked at March 31 had injury at a level of about 10 percent. For more information on the topic refer to "Freeze Injury On Wheat".
Powdery mildew has been found in several wheat fields in Tom Green County. Several producers have made fungicide applications to correct the fungi's development.
Losses from powdery mildew is not as extensive as severity of symptoms indicate. Powdery mildew is easy to identify. The first symptoms are light green flecks on the leaves. Very soon white tufts of fungus develop. These tufts spread over the leaf and turn to a dirty gray mat. Dusty white spores are produced in great numbers and cover leaves and soil. Affected leaves turn yellow and die. Under some conditions, distinctive spots of dark green persist in yellowing leaves. The disease increases respiration and water loss and decreases chlorophyll; consequently, photosynthesis declines.
Powdery mildew is caused by the fungus Erysiphe graminis f. sp. tritici. Closely related forms cause powdery mildew on many grasses. These forms are closely adapted to their specific hosts so it is doubtful if there is much cross-infection from other crops and grasses to wheat.
The fungus survives on dead wheat plants and within infected leaves. Fall infection can occur, but the main concern is usually in the spring near the time of jointing. Lower leaves are infected first and it progresses up the plant, leaf by leaf, as long as conditions for spore production and infection persist.
Powdery mildew thrives in cool damp conditions. Optimum temperature for growth is 68 degrees Fahrenheit (F) with relative humidity near 100%, but heavy rain actually reduces it. Spores survive about two days at 70 degrees F and considerably longer at cooler temperatures. This permits some long distance dispersal by wind. Some infection can occur as low as 40 degrees F. Epidemic development stops abruptly about 75 to 80 degrees F. This often prevents severe loss since infection of the top two leaves is necessary for significant yield effect and it is usually warm enough by the time these leaves emerge to prevent extensive infection. Powdery mildew is most prevalent in low lying, thickly planted fields protected from wind and heavily fertilized with nitrogen. Only slight differences in fertility or plant density can cause drastic differences in disease severity within a field.
Since high fertility and thick planting are necessary for maximum yields, cutting back on these to control powdery mildew is not practical. There is no clear indication that cropping sequences or residue management affect powdery mildew severity.
Resistant varieties have been developed in areas where powdery mildew is more serious. Our present varieties range from moderately resistant to very susceptible with none highly resistant.
Fungicides that are highly effective against powdery mildew have been developed, however, the erratic nature of powdery mildew combined with low wheat prices make regular use of fungicides uneconomical.
The minimum soil temperature for planting cotton is a 10 day average of 60 degrees F at an eight inch soil depth taken at 8:00 in the morning. When soil temperatures are 65 to 70 degrees F the cottonseed germinates and emerges quicker which helps to reduce the amount of time emerging seedlings are exposed to soil diseases. If cotton is planted at the minimum soil temperature and then watered, you will probably have a reduction in the final plant stand and health of the crop.
From result demonstrations conducted in Nolan and Mitchell Counties over a five year period, the ideal planting rate is 4 to 5 seeds per foot with a final plant stand of 3 to 4 plants per foot. This is true for both dryland and irrigated cotton. If everything goes according to plan, the cottonseed for District 6 & 7 should be available for pick-up by the end of April. A copy of the proposed variety tests to be established is attached.
The information used for the Extension agents training on cotton can be accessed at the following URL http://sanangelo.tamu.edu/agronomy/cotton/cotton.htm. The information covered on Result Demonstrations can be accessed at the following URL http://sanangelo.tamu.edu/agronomy/resultdemo/index.htm.
On Monday, April 14, there will be a training conducted at Abilene for producers needing to obtain a Private Applicators License. For more details and to register for the meeting call Gary Bomar at (915) 672-6048.
An Agricultural Waste Pesticide Collection Event has been scheduled for April 4, 2003 in Snyder; April 7, 2003 at the Farmer's Co-Op Gin of Stamford; April 9, 2003 at Wall CO-OP Fertilizer Facility; and April 11, 2003 in Mason. Collection of materials will be from 8:00 a.m. to 1:00 p.m. For more information go to the TNRCC Website (http://www.tnrcc.state.tx.us/exec/oppr/agwaste/agwaste.html).
Several of you conduct grain sorghum and forage sorghum variety tests each year. Sometimes these demonstration plots are short fused with varieties needed quickly. [Click Here] for a list of most of the companies that cooperate with us in result demonstration work. By selecting varieties from the same maturity group you will save yourself a lot of problems.
Several agents indicated that it would be useful to have the weeds grouped by bloom color. In an attempt to get started, compiled is a list of weeds that will have white blooms in the spring. Each small picture is linked to a larger picture. Let me know if this is what you asked for.