- Monitoring Lygus in cotton
- Stripping alfalfa hay
- Movement of Lygus in the Landscape
- Natural enemies in cotton
With growing conditions continuing to look favorable for cotton growth and development, fruiting is beginning or well underway in some locations. Fruiting is being noticed in Firebaugh area at 6th main stem node, which is line with early season temperatures we have experienced and good planting dates.
Setting the early fruit sets the plant up for the rest of the season. With a shortage of the irrigation deliveries this year, the season must be as compact as possible. Protecting early fruit is critical in these water short conditions.
Lygus will be a localized problem. Movement will occur from neighboring sources, most likely other cultivated crops. Key sources for Lygus include safflower, forage alfalfa and seed alfalfa. Within safflower and alfalfa forage, the Lygus population can be managed to prevent mass movement into surrounding cotton fields. Lygus is closely managed in seed alfalfa can still acts as a major source.
Safflower is currently being treated for Lygus to prevent the first generation from
Alfalfa forage is the most common crop which Lygus prefers. It is a unique crop in our cotton landscape because it is harvested frequently for its vegetative biomass, not its reproductive parts, e.g. fruit, lint, seed. Providing even a limited habitat during cutting can have a substantial effect on mitigating Lygus movement into cotton. During the June and July cuttings, if uncut strips of alfalfa are left in the field, Lygus will move to them and stay until the next irrigation cycle, when they return to the larger alfalfa field.
Limiting the movement of Lygus into cotton not only protects the fruit during this critical early stage but can reduce the need for insecticide applications. This allows additional natural enemies to build and helps reduce pressure for the development of insecticide resistance.
Early intervention through the cultural control of Lygus source management will help set the cotton up for high fruit retention, shorter season and fewer secondary insect and mite problems, as well as reduce costs in early insecticide treatments.
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
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.
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
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.
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.
The large amount of rainfall this winter and spring will set the stage for more Lygus in summer. The relationship between historic rainfall records and annual cotton loss estimates supports the idea that Lygus will be more problematic this year and observations from the ground confirms this assessment. However, as in other years, the primary source of Lygus will be from crops and locations within a few miles of your cotton field, not miles away from the edge of the Valley.
In the past month, I have been conducting the annual Lygus survey. The survey was later than usual because of the extended rainy season into April and cooler temperatures in May. This is what I have observed:
- Foothills are generally dry and limited Lygus hosts, due primarily to early rains that favored grasses over broadleaves. 2011 was not a great year for wildflowers in the Sierra foothills due mostly because of the heavy grass prevented the annual broadleaves from developing widely.
- Along the I-5 corridor, tarweed, a key indicator host for Lygus, is located mostly south of Highway 198. It is more common on the valley flats than on the coastal foothills. When sampled 2 weeks ago, the population was split between overwintering adults and first generation nymphs, 1st to 3rd instars. The further south I travelled the more tarweed I could find in uncultivated areas of Kern County, commonly known as “deserts”. The importance of tarweed is not as much it is a major source for the Valley but rather as local infestation point and indicator of potential problems.
- Tarweed is a good plant for Lygus development because it spans the late winter and summer periods. It acts as a bridge for Lygus to develop a foothold and increase its numbers during May and parts of June. Without that bridge, populations tend to disperse and build slower and later.
Safflower plays a major role as a plant host bridge, allowing overwinter populations to settle and reproduce. Safflower plantings are spread throughout the Valley and will act as localized sources for Lygus into susceptible crops. The problem can be alleviated by managing Lygus population in safflower before the nymphs can become adults and leave the field. For details on managing Lygus in safflower to mitigate movement into cotton, refer to IPM in Cotton in the Western Region of the US, UC ANR Publication 3305.