March 1, 2005


The rain we have gotten this year has been greatly appreciated. The potential for rust is very high this season and we should be prepared to answer questions concerning stripe, leaf and stem rust. As air temperatures increase this spring, the wheat plants will begin to grow rapidly, in acreage where adequate nutrients are available. Both stripe and leaf rust have been active in the Uvalde area this season. The fungi that causes rust can easily move on wind currents and arrive in our area. The severity of the rust will be determined by the environmental conditions.

Questions #1 and #2. What is the difference between leaf, stem and stripe rust? What environmental conditions are needed for the developement of each?

Leaf, Stem and Stripe Rust

Most producers are familiar with leaf rust and stem rust which can cause extensive damage. The fungi which cause these diseases, when left unchecked in favorable environmental conditions, can result in the loss of both grain yield and quality. The development of the fungi is impacted by water and temperatures. When favorable environmental conditions exist the life cycle for the spores can occur in 7 to 14 days. Frequent heavy dew, light rain, or high humidity and temperatures generally in the range of 59 to 77 degrees Fahrenheit (F) are ideal for rust development. Pustules form on the surface of the plant parts and contain thousands of microscopic spores. The pustules erupt releasing the new urediospores into the air and they are dispersed by the wind.

Urediospores germinate in rain or dew and infect leaves within 6 to 8 hours after settling on the plant surface. The infection element of the fungi is capable of penetrating into a plant directly or will enter through the plant's breathing pores or wounds. Plants have many microscopic breathing pores called stomata on the surface of the leaves. This is a common spot of infestation. Once the fungal infestation element becomes established inside the plant, the invaded tissue gradually dies as the urediniospores develop. Shown in Figure 1, is the urediospores of leaf, stem and stripe rust. Rust spreads by wind blowing urediospores from plant to plant and from field to field until the crop matures.

Leaf Rust

Stem Rust

Stripe Rust
Figure 1. Urediospores of leaf, stem and stripe rust.

Stripe rust (Puccinia striiformis)
Stripe rust is blown into our area by prevailing winds. Winds can carry rust spores for great distances. The disease can develop rapidly when moisture is not limited. Urediospores are yellow to orange in color and have an elongated shape. Urediospores lose their viability rapidly at temperatures above 59 F. Germination is best between 41 and 59 F, with limits at 32 and 68 F. Infection may occur through the winter since the mycelium remains viable to 23 F. The disease develops most rapidly between 50 and 59 F when intermittent rain or dew occurs. Many disease cycles may take place in one season, since the time between infection and sporulation under optimal conditions is about 8 days. Cool, wet falls; mild, open winters; and long, cool, wet springs favor stripe rust.

For more information about stripe rust and fungicide recommendations (click here).

Leaf rust (Puccinia recondita)
Leaf rust is blown into our area by prevailing winds. Winds can carry rust spores for great distances. The disease can develop rapidly at temperatures of 52 to 72 degrees F, when moisture is not a limiting factor. The optimum temperature for sporulation and infestation is approximately 70 degrees F and infestation can occur within four hours if leaves are wet. The spores can initially infect and produce pustules where the raindrops have collected at leaf axils and tips. New pustules erupt within 7 to 10 days. Rust development is slowed drastically with cooler temperatures or a shorter leaf wetting period. At 60 degrees F, a wetting period of 8 to 10 hours is necessary. Very wet conditions reduce spore dispersal. Epidemics generally develop when favorable moisture exists and temperatures are above 60 degrees F.

Leaf rust pustules (uredia) develop primarily on the upper surface of leaf blades. Pustules are round to oval, about 1/50 inch in diameter (about the size of a pinhead), and filled with thousands of orange-red spores (urediospores). These spores are easily dislodged by the wind or rubbing and accumulate as red dust on hands, clothing, and machinery. They may occur on stems but are most common on the upper surface of the leaves. Rust increases water loss from leaves so they die prematurely.

Since the leaf rust loss results from the early kill of the upper two wheat leaves, the faster an epidemic develops, the greater the loss. Loss can be roughly predicted by matching severity on the flag leaf with growth stage. If the flag leaf is severely damaged prior to the milk stage, the approximate loss in yield is 25 to 40 percent. If the disease damages the flag leaf between the soft and hard dough stages of the developing wheat, yield losses are usually less than 10 percent.

Stem rust (Puccinia graminis)
A wave of infection usually advances northward by wind-blown spores released from infected wheat or barley plants. Stem rust usually enters our area in late March to mid-April depending on weather conditions and the extent of disease development on cereal crops south of us. The disease usually appears on plants in early spring.

After infection, pustules form in 7-10 days. The pustules break open, releasing masses of spores that can infect surrounding plants. Temperatures of 68 to 77 degrees F favor stem rust development. Rust spots are very small, circular or elongated, and vivid orange-red in color. Later in the year, the rust pustules darken because of the production of dark-brown-black spores which are the overwintering stage of the rust.

Infected plants usually produce fewer tillers, set fewer seeds per head, and yield small shrivelled seeds with poor milling quality and food value.

Question #3. How does a late spring freeze injure wheat?

A cold front with freezing temperatures is not uncommon in the wheat production regions of Texas. As the wheat starts to grow in the spring, it becomes more sensitive to low temperatures. It only takes about two hours of cold temperatures to injure the wheat. A publication on the topic of freeze injury in wheat is (linked here).

Question #4 was asked by Jerry Kidd, McCulloch County Extension Agent. How long should I wait before grazing after applying fertilizer to wheat?

To determine how long to wait before grazing wheat after a fertilizer application you need to consider: 1) the rainfall or irrigation received after the fertilizer is applied and 2) the growing conditions that occur after the fertilizer application.

It is best to wait for the fertilizer to be washed of the foliage by rainfall or irrigation. This allows the fertilizer to reach the soil surface and to become attached to the soil or converted to a form used by the plant. Once this occurs the livestock can begin grazing again. However, if growing conditions are poor (for example cool, cloudy, dry conditions) after fertilizer application, there can be an accumulation of nitrate in the forage, which can be toxic to livestock. In this case, it is important to wait until good growing conditions return to allow the wheat plants to convert the nitrate to plant protein.

Also, remember to condition the livestock before allowing them to begin exclusive grazing of the high quality forage, otherwise, you may have a lot of bloating occur which can result in the death of the animal. The nitrogen levels in wheat plants peak around 14 days after the nitrogen is applied, declining gradually over a period of weeks. Plant nitrogen is in a soluble form in the re-growth soon after fertilization. Animals should not have access to the wheat for at least 21 days after the nitrogen fertilizer is applied.

Question #5. Because of weather delays I have not had a chance to control the wild oats growing in my wheat. Is it to late to apply herbicides in late-February or early-March?

I would be concerned with the size of the wild oat plants and the potential injury to the wheat from the herbicide applied. Puma and Osprey herbicide can give a high level of wild oat control up to the 2-tiller stage, if the wild oat plant has not been stressed by limited soil moisture. Apply the herbicide exactly the way the label indicates. To read the herbicide label go to and type in the herbicides name. For more information about about wild oat control refer to the linked publication Wild Oat Control In Texas.


The following counties have contacted me about cottonseed for 2005 tests: Glasscock, Howard, Jones, Reagan and Upton. I will be calling companies soon to make seed request.

The information from the remaining cotton variety tests is linked to the county name. The other test results were reported in last months newsletter. Information from the 2004 test in Howard County, Jones County, and Tom Green County is now available.

With the high lint yield obtained in 2004, combined with rain since harvest, producers need to submit soil samples from fields to be planted this spring. If a producer has 20 pounds of available nitrogen in the upper 6 inches of soil this will meet the cotton's need until the one-third grown square stage. However, I'm not sure that we even have 20 pounds of nitrogen per acre in the upper foot of soil. This lack of nutrients can be detrimental in establishing a healthy crop. A soil analisis will keep you from applying more nutrients than necessay. By getting the soil analized early, soil applied fertilizer can be used instead of the more expensive foliar applied.

Question 6#. What is the proper planting rate for cotton?

The planting rates of cotton should be based on a target plant population. If the acreage is irrigated then the desired plant population is three to four plants per foot on 40-inch rows. Higher planting rates increase seed costs, have adverse effects on yield and quality, and intensify seedling disease problems.

Under favorable dryland conditions, a plant population of two to three plants per foot is sufficient on 40-inch rows. Seed size varies among varieties and should be considered when planting. Under dryland conditions, any stand greater than 45,000 plants per acre (3.4 plants per foot on 40 inch rows) is excessive.

For more information about raising cotton refer to this linked publication

Question 7#. When should I plant cotton?

It is important to have a warm soil to plant the cottonseed into. The minimum soil temperature for planting cotton is a 10 day average of 60o F at an eight inch soil depth (take temperature at 8:00 a.m.). When soil temperatures are 65 to 70o F the cottonseed germinates and emerges quicker which helps to reduce the amount of time emerging seedlings are exposed to soil diseases. Also, 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.

For more information about raising cotton refer to this linked publication

Question 8#. What is an acceptable level for Free Fatty Acid content in cottonseed kept for planting?

There are several measurements available to determine seed quality. All give a good estimation of quality, but measure different aspects. When all the tests are used in conjunction with each other, a true picture of seed quality is apparent. Free fatty acids (FFA) alone only serves as a rough estimate. In general, cotton seed that contains less than 1% FFA are considered good quality, but seed testing 1.5% or higher may be weak. If the FFA content is above the 2-3% level, something has caused the seed to deteriorate. The standard germination test that is performed on all cotton seed is conducted under ideal conditions. Eighty percent germination seed should produce an 80% stand under warm, ideal planting conditions. It is possible to have low FFA seed with a good warm germ, and still have poor vigor seed.

Generally if planting conditions are poor with marginal soil temperatures, then seed with the highest possible Cool-Warm Vigor Index (CWVI), should be planted. As conditions improve and become more conducive to stand establishment, lower quality seed can be planted. The Cool-Warm Vigor Index, developed by Dr. Norman Hopper--Professor of Seed Physiology at Texas Tech, is a measure of the seed's germination, and vigor. The CWVI is a combination of the warm germination test results (obtained from counts after four days of incubation) and results from a cool germination test (results obtained after seven days of incubation). Seed lots with an index of 160 or greater have "Excellent" vigor, 159-140 is "Good"; 139-120 is "Fair" and less than 120 is "Poor". Generally if planting conditions are poor with marginal soil temperatures, then seed with the highest possible CWVI should be planted. As conditions improve and become more conducive to stand establishment, lower quality seed can be planted. The Texas Department of Agriculture's Seed Laboratory in Lubbock will perform the germination tests for a fee.

For more information about raising cotton refer to this linked publication

Pesticide Recertification Training

On Monday, March 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 (325) 672-6048.

None of the Agricultural Waste Pesticide Collection Events currently scheduled for 2005 are going to be conducted in our area. For more information go to the Texas Commission on Environmental Quality (TCEQ) Website that is linked (

Grain Sorghum and Forages

Several of you conduct grain sorghum and forage sorghum variety tests each year. Sometimes these demonstration plots are short fused with varieties needed quickly. By selecting varieties from the same maturity group you will save yourself a lot of problems. Two main problems that can be avoided is timing insecticide applications and harvesting the plot within a short time frame.

From the variety tests conducted over the past five years, we have found that producers management practices have the greatest impact on the quality of forage being harvested as hay or forage. Before spending a lot of time and effort on a variety test, you need to select a producer that has good management practices.

Question 9#. What is the proper planting rate for grain sorghum?

Under dryland conditions, the planting rate on 40-inch rows should not exceed 2 to 3 seeds per foot (26,000 to 39,000 seed per acre). Dryland production using a "skip row" planting pattern should use about the same number of seed per row foot. When narrow rows are used under adequate irrigation, you would still have the same seed population per acre; however, the number of seed per foot of row should be adjusted accordingly. On 40-inch rows with limited irrigation, 5 to 6 seeds per foot are sufficient, and to produce maximum yields with full irrigation plant 8 seeds per row foot.

For more information about raising grain sorghum refer to this linked publication

Question 10#. When should I plant grain sorghum?

It is important to have a warm soil to plant the grain sorghum seed into. For highest yields, and to avoid possible sorghum midge damage, plant as soon as soil temperatures reach a minimum of 60 degrees F at planting depth (reading should be made between 7:00 and 8:00 a.m.). For the Southern Rolling Plains of Texas the optimum planting dates begin in early April. Yield reductions can be expected from plantings made after June 15 due to sorghum midge damage, inadequate precipitation, heat stress and other climatic events.

For more information about raising grain sorghum refer to this linked publication

Weed Identification

Several agents indicated that it would be useful to have the weeds grouped by bloom color. Linked are pictures of weeds sorted by bloom color. Weeds that have yellow blooms, white blooms, and purple blooms in the spring. Each small picture is linked to a larger picture.

If you haven't seen the plant ID site at Uvalde, I linked up there ID by flower color pages. They have pages for Red, White, Blue and Yellow flowers.

Monthly Calendar


March 1, Tom Green County, Concho Valley Cotton Conference
March 7, District 7 Office, Office Conference
March 18, Tom Green County, Professional Ag Workers
March 22, Brown County, Brown County Ag Day
March 24, Burnet/Llano Counties, Plant Growth and Development
March 25, Howard County, Cotton Production Meeting
March 29, Jones County, Multi-County Cotton Conference
March 30, Scurry County, Multi-County Cotton Conference


April 4, District 7 Office, Office Conference
April 5, San Saba County, Forage Conference
April 6, District 3 Office, SWRES Meeting
April 7, Lubbock County, Symposium on Cotton
April 8, Brazos County, Tenative
April 14 & 15, Brazos County, Annual Leave
April 26 & 27, Brown County, Professional Board Meeting
April 28, District 7 Office, Natural Resources Field Day


Billy E. Warrick
Extension Agronomist
Texas Cooperative Extension
Texas A&M University System