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September 18, 2019 Vegetable IPM Updates
 
 
 
Insect Management
Diseases
Weed Science
Plant Diagnostics
Biometeorology
 
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Insect Management:


They’re Back……….Let the Produce Season Begin

In the past few days I’ve observed and received reports from PCAs of key insect pests beginning to show up regularly on Yuma produce. Not surprising given that cabbage and cauliflower transplants have been in the ground now for several weeks, and early-planted broccoli and lettuce stands are established. Here is what I’m hearing and seeing:

Bagrada bug: Starting to show up in light numbers at the Yuma Ag Center (YAC) on broccoli and cauliflower transplants. More than we’ve seen in the past few years. We estimate the population is below threshold, but we have been seeing more adults and damage show up every day. Perhaps more importantly, I’ve had numerous PCA/grower reports over the past week of bagrada bugs found on both transplanted and direct seeded crops throughout the area including Texas Hill, Roll, Wellton, Dome Valley, Gila Valley, Yuma Valley and Bard. Just about everywhere. These are populations that over-summered and are likely coming out of cotton, alfalfa, bermudagrass, Sudan grass and weedy areas. The winter/spring rains that provided abundant mustards and weedy habitats for other plant bugs (e.g., Lygus, false chinch bug) appear to have also benefitted bagrada bugs this summer. So far populations have been relatively light compared to past years but based on previous research (see graph below), this is about the time bagrada begin to appear. The next two weeks will be telling as acreage increases; bagrada generally peak in late Sep and early Oct so keep your eyes peeled for damage and adults on seedling cole crops. This may just be the beginning. More information on bagrada bug management on can be found in: Bagrada Bug Management Tips for the Low Desert 2019.

Lepidopterous Larvae (worms): Right on schedule, beet armyworm larvae are showing up in heavy numbers on 12-day old lettuce. Can easily find egg masses, 1st and 2 instar larvae on seedlings with 1-2 leaves. Similar reports are coming in from PCAs of armyworm on most produce crops. Larvae are said to be heaviest in Dome Valley and Wellton which is consistent with our moth trap catches in these areas. (see Area-wide Insect Trapping Network). Have also had multiple reports of corn earworm showing up on the early produce crops, and this is also reflected from trap catches to date. Cabbage looper larvae have not be observed at YAC, and only one or two reports from PCAs. Trap counts are also low, but still a little early for them. Diamondback moth: So far, no reports of diamondback moth in transplanted or direct seeded crops in Yuma area. Area-wide trap counts are very low; lowest we’ve seen in the past 3 years at this time (see Area-wide DBM Trapping Network). Lack of monsoon storms may partially explain this. Received a report from Imperial Valley last week of cauliflower transplants arriving from coastal California infested with DBM adults and larvae. If you receive transplants with larvae and adults, you should watch those fields closely and treat accordingly. We recently bioassayed a DBM population collected from Salinas in August that was resistant to Coragen, thus it is advised that you avoid using Coragen for DBM control, particularly on transplants originating from outside the desert. For more information of managing DBM on fall crops see 2019 Guidelines for Diamondback Moth Management in Fall Cole Crops. Note: Even though the weather forecast is calling for cooler weather with highs around 100 and lows in the 70’s for the next 2 weeks, don’t relax. These average temperatures (~86 °F) are optimal for biological development of bagrada, armyworm, loopers, DBM, flea beetles and whiteflies. Furthermore, these cooler nights will not discourage adult moth flights and egg lays. We’ll have to wait until it gets cooler in October for that to happen.


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Can you ID the insect below?

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Remember, When in Doubt . . . . . “SCOUT”

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To contact John Palumbo go to:jpalumbo@ag.arizona.edu
Diseases:


Managing Sclerotinia Drop of Lettuce With Fungicides 2019

Successful management of any plant disease is achieved by targeting one or more vulnerable stages in the disease development cycle. For Sclerotinia drop of lettuce, caused by the fungi Sclerotinia minor and S. sclerotiorum, this point of attack would be the dark fungal structures called sclerotia. At crop maturity, sclerotia produced on infected plants by these pathogens will be incorporated into soil along with crop debris as the field is prepared for planting the next crop. Sclerotia serve the same purpose that seeds do for plants; that is, they allow these fungi to carry over in soil in a dormant state until conditions become favorable for their germination and growth. Over the past several years of fungicide evaluation trials, one or two fungicide applications to the bed surface beginning at seeding or after thinning have provided at best a 50 to 60% reduction in dead plants compared to plots not receiving fungicide treatments. In a comparison of fungicide efficacy data from 2011 to 2016 field trials, the average reduction of dead lettuce plants on beds containing Sclerotinia minor was 54, 52, 43, 42, 39, 31, and 30%, respectively, for plots treated with Endura (boscalid), Merivon (fluxapyroxad + pyraclostrobin), Fontelis (penthiopyrad), Kenja (isofetamid), Rovral (iprodione), Cannonball (fludioxonil), and Contans (Coniothyrium minitans). On beds infested with Sclerotinia sclerotiorum, the mean reduction of dead plants in the same six trials was 63, 55, 51, 45, 41, 40, and 23%, respectively, for plots treated with Contans, Merivon, Kenja, Rovral, Endura, Cannonball, and Fontelis. These data show that the degree of fungicide effectiveness often depends on the species of Sclerotinia present in soil. However, for both species of Sclerotinia, application of fungicides to the bed surface will prevent germination of sclerotia at or near the soil surface, thus reducing lettuce plant infection and death

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To contact Mike Matheron go to: matheron@ag.arizona.edu.
Weed Science:


Cultivation Is Not a Good Method to Control Purslane

Common Purslane reappears year after year even in fields where it has been well controlled the previous season. There are a couple primary reasons for this, one is fairly easy to minimize and the other is not. The easy one is to stop relying on cultivation to control it. Purslane is a succulent with stems and roots that can survive for several days, reroot and produce seed. Purslane loves newly cultivated open fields where broken stem and root pieces can reroot. The leaves are waxy and have small stomata to help it survive dry conditions for a long time. Some people grow purslane as a microgreen, and they like to plant it by breaking plants into pieces and spreading them on the surface. The seeds also germinate well on uncovered soil surfaces. The more difficult to control reason that Purslane reappears year after year is that it produces a lot of very small seed that can float and blow long distances. It has been reported that one plant can produce tens of thousands of seeds that can survive in the soil for as long as 40 years. Crop seed is developed to all germinate at the same time while weed seed survives because it doesn’t. Some of the seed that germinates in the field was there already and some has moved in in water or wind. The best method to control purslane is to spray it when it is small (inch or less) with a combination of a systemic and a contact herbicide to kill the roots and rapidly desiccate the leaves and stems.
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To contact Barry Tickes go to: btickes@ag.arizona.edu.
Biometeorology in IPM:


Leaf Wetness Update

Growers and PCAs can monitor data from the Yuma Leaf Wetness Network through the AZMET website located at the following URL: http://128.196.12.122:460/


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To contact Paul Brown go to: pbwown@ag.arizona.edu.
Plant Diagnostics:


Plant Diagnostic Resources - Sep 18, 2019

We are gearing up for 2019/2020 growing season. Apart from the common disease problems like Fusarium wilt, Downey mildew, Sclerotinia we came across few mystery ‘disease’ problems past growing season. Listed are couple interesting ones to look out for this season. Lettuce crown galls About 50% of the lettuce plants in the field had a gall in the crown area. In some cases there were little lettuce plants emerging out of the gall. The sample came out negative for fungi, bacteria, virus, viroids after performing isolation, molecular diagnosis and high throughput next generation sequencing. The ‘verdict’ was it could be residual effect of something that was sprayed in the past season. However, keep an eye on symptoms and notify us immediately so we can get to the root and crown of the problem. See pictures.

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‘Sooty’ mold in kale Almost 100% plants in the field had symptoms. No sign of pathogen in the tissue, nothing was isolated, the symptoms got worse in less than a week. After collecting information from diagnostician all over the US and Canada it was narrowed down to ‘pepper spots’. Pepper spots is commonly observed in Chinese cabbage. The exact cause is unknown and seems like is a combination of genetic and environment. High nitrogen level and high pH are reported to worsen the symptoms. (https://edis.ifas.ufl.edu/pdffiles/HS/HS35200.pdf) If you happen to see any similar symptoms in your field, please let us know. We would like to investigate more.

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To contact Bindu Poudel go to: bpudel@email.arizona.edu.
Other:

Real IPM
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Send your questions to:
CALS-Yuma-AZVegIPM@email.arizona.edu
Links:

The Vegetable IPM Updates Archive page provides links to updates from previous weeks.

The Vegetable IPM Video Archive page contains a collection of educational videos from current research work in vegetable crops by University of Arizona Researchers.

 


For questions or comments on any of the topics please contact Marco Pena at the Yuma Agricultural Center.
College of Agriculture, The University of Arizona, Tucson, AZ.


 
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