Cotton planting is well underway in the past 3 weeks now that the weather turned warm. While the initial planting was cool and intermittently wet, temperatures since April 16^th in the San Joaquin Valley have been excellent for planting cotton. Looking at temperature conditions from March 1 to April 26, 2012 according to accumulated degree-days > 60◦ F five days after planting, Shafter and Five Points had 47% and 37% of those days in the Adequate to Ideal categories (Figure 1). 

Figure 1 (click to enlarge)

Since April 15^th, all dates have had ideal heat accumulation five days after planting (Figure 2A). These data are based on actual temperatures rather than forecasted data. While the forecasted (predicted) degree day accumulation 5 days post planting varied from actual temperature recordings, this year it under-estimated the degree day total (e.g. more conservative) more than it over-estimated (Figure 2B). Some of the the difference can be attributed to inaccuracy in predicting temperatures five days out and the generalized nature of forecast as compared to actual site recording. 

     

The cotton is germinating and emerging from the soil very nicely. In the warm days since April 15^th, most cotton should have germinated 10-14 days after planting. Getting a good, vigorous stand is a fundamental step in developing a season long IPM plan. Assessing your stand to determine the number of plants/acre is a useful indicator to address replant concerns and future management decisions. Guidelines for assessing your stand can be found by clicking here on Cotton Year Round IPM site. 

Cotton planting season for cotton is already upon us. Planting cotton into the most favorable temperature conditions results in good stands and vigorous plants. The 5-day forecast of degree-days (heat units) is provided to help California's San Joaquin Valley and Sacramento Valley cotton growers determine suitable weather to plant cotton and avoid chilling injury to emerging cotton seedlings. Healthy, vigorous plants are a good foundation of an IPM Program.

UC Cooperative Extension, UC IPM Program has been providing cotton planting forecast to cotton growers and PCAs for over 20 years. The system is now available for the 2012 season. This forecast, with the planting guidelines, should be used in conjunction with soil temperatures (at seed depth) above 58°F for timely, vigorous seedling establishment.

The degree-day forecasts are based on the best available weather forecast from National Weather Service. However, local conditions may cause some variation. Use your judgment if your local temperatures are different. If your min/max temperatures are above those reported, then your degree-days will be higher; if your min/max temperatures are below those reported, then your degree-days will be less.

Planting Guidelines using 5-day
Degree-Day Forecast

Forecast Degree-Days	Planting Conditions
> 20	Ideal
16 - 20	Adequate
11 - 15	Marginal
< = 10	Unfavorable

 The degree-day accumulations are calculated using the single-triangle method and a lower threshold of 60°F with no upper threshold. Forecast temperatures were accessed from the National Weather Service Web sites for Hanford and Sacramento.
 
   In 2004, an evaluation of the accuracy of UC cotton planting forecasts for 1998 through 2002, for Bakersfield and Fresno was published in California Agrculture and showed:

• In March, planting only on days with ideal category forecasts (which occurred on 25% of March days), can likely avoid the need to replant due to incorrect forecasts predicting favorable planting conditions.
• In April, following the forecast is quite safe, since it failed to predict unfavorable planting conditions (which occurred on 29% of April days) on average only 1 day out of 30 April days.

See the article for details.

Gathering in a cotton field near Mendota, CA, farmers, pest control advisers and UC Cooperative Extension gathered to discuss approaches to the challenges in cotto

n production in the next few weeks. Sponsored by the Sustainable Cotton Project (SCP) and UCCE, the participants shared their experience, opinions and suggestions for dealing with key issues in the next few weeks. All agreed that it is essential to set as much fruit in the next few weeks as possible and that the greatest threat is Lygus feeding on young fruit.

Three main factors for Lygus management need to be considered: 

What is the source?

Is it a strong source such as safflower or seed alfalfa which produces large numbers of Lygus as the crop is prepared for harvest? Is it alfalfa hay which can mitigate the movement of the pest if habitat is preserved? Is it weaker sources like tomato or other poorer hosts which produce far fewer?

How far from the source is the field? The greater the distance from the source, the less the threat. Even the strongest sources have a limited sphere of influence, perhaps no greater than 2 miles.  

How many Lygus are in the field and how much threat do they present?

It is essential to frequently monitor and record the cotton fruit retention as well as the population density of Lygus bugs. Both are critical for making the best decision. Small numbers of Lygus in a field with poor retention is a greater threat than a larger population in a well fruiting field. Remember the cotton integrates all stress, bugs or weather, and reflects that in current fruiting conditions  See details in Field Check link below.  

What to use to control Lygus?

Chose your material carefully to limit resistance pressure on the pest target. Understand IRAC mode of action labels and utilize rotation of active ingredients. Start with the most selective products to preserve your valuable inventory of natural enemies and avoid secondary outbreaks of aphids, mites or whiteflies. Move to more broad-spectrum insecticides later in the season. For a summary of UC IPM Guidelines for Lygus, see link below.

Group consenus

All ageed that the next four weeks is the critical period for setting fruit and establishing yield. They also noted that 2011 is only slightly behind 2010 which was a good year, yield-wise. Good management, including conscientious monitoring and decision making for Lygus can go a long way in setting up the remainder of the year.

Finally, most agreed that time spent checking your fields is an investment, not an expense.

For over 20 years, UC has recommended plant based measurements as a basis for production decisions. These decisions include timing for Lygus treatments, using plant growth regulators, determining crop cutout and planning for defoliation. Details are

available from the Cotton Production Manual, UC ANR Publication 3352.

Why use plant based measures? Think of the plant like a patient in the physician’s office. Often questions that the doctor asks helps guide us toward a treatment. Likewise the cotton can tell a story, if you know how to read it.  For Lygus management decisions, there are three key features; the age of the plant (number of fruiting branches), the early fruit (retention of fruit on the bottom five fruiting branches) and the current fruit load (retention of fruit on the top five fruiting branches).

The cotton plant cannot lie about previous stress it has suffered, including cool weather, early insect damage, poor irrigation timing or heat. Competition within the cotton plant for
resources is One stress we often ignore. Cotton produces more fruit than it can
mature because it produces fruit as insurance for its species survival. Thus,
as the season progresses, fruit is less likely to be retained under normal
yield loads. We know this because we measured it and can provide predictive
guidance about the probability of any fruit being maintained to harvest.

If you know the age of the plant, the current fruit load on the bottom and the current fruit load in top, you can determine whether your current retention is greater than expected (see table). If fruit was lost early, regardless of the cause, the current top fruit is more valuable and should be retained.

Coupling the expected fruit retention with Lygus population density  estimates from sweep counts, a good interpretation can be made regarding the threat of that population. If fruit is predicted to drop anyway because of existing fruit load, more Lygus can be tolerated. See complete instructions and calculator at  www.ipm.ucdavis.edu/PMG/C114/m114mklygusdecisn.html.

Letting the cotton plant tell its story is essential for setting treatment thresholds for Lygus. The threshold is dynamic depending on crop condition, age of the plant, time of year and surrounding sources for pests. Please go to cottoninfo.ucdavis.edu/IMAGES/FieldCheck_June_2011.pdf
and download,   Using Plant Based Measurements to Support Lygus Management Decisions.