As cotton seedlings develop, western flower thrips (WFT) can occur in great numbers.  As winter grain fields  dried up for harvest or alfalfa fields are cut for hay, large numbers can descend on a cotton field causing growers and PCAs to pause and wonder, who goes there, friend or foe?

FOE: Western Flower Thrips feed on young leaf tissue causing the leaves to distort and curl. If present in sufficient populations, they can feed and destroy the growing meristem region, setting back the development of the plant. Such damage occurs during extended of cool temperatures during the seedling stage. In most years, the growth rate of cotton will outpace the damage caused by thrips to the leaves.

FRIEND: Western Flower Thrips is a key natural enemy to spider mites. Seeking mite eggs, WFT will move through mite webbing and consume many mite eggs in a day. In addition, they became an important prey base for general predators such as minute-pirate or big-eye bugs.

Under current conditions, it is unlikely that WFT will present any threat to developing cotton seedlings and will provide valuable ecological services to your farm. Early treatments are mostly unnecessary and interfere with the annual development of the cotton food web that is developing within your fields.


For more information, go to UC IPM Website by clicking here.  

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.