Research and Extension

Potatoes at WSU

2013 Potato Insect Pest Survey for the Columbia Basin of Washington

Aphids, Leafhoppers, Tuberworm, and Psyllids

The insect pest survey provides the potato industry with current information about the size and location of important insect pest populations in the Columbia Basin.


INSECT MONITORING REPORTS
Report for August 16, 2013

BEET LEAFHOPPERS (BLH)   

We are seeing a lot of purple top in the Columbia Basin. It looks just like zebra chip in the foliage, but when you cut into the tubers there are no symptoms. It is not surprising that we are seeing more purple top this year versus the last few seasons, because BLH numbers on sticky cards have been much larger compared to the previous few years. Potato plants that are infected with BLTVA while they are still small are particularly susceptible to developing symptoms. This week, we found BLH at 95% of our trapping sites across the Columbia Basin. Their numbers are increasing again. However, mature plants have been shown to be less susceptible to BLTVA infection compared to younger plants.

Beet leafhoppers are important pests because they transmit BLTVA, a phytoplasma that causes purple top disease in potatoes. In the Columbia Basin, the first spring generation of BLH usually migrates towards potato fields in late May and early June, with a peak flight in late June. Yellow sticky traps placed near potato fields are one way to monitor BLH. Information about setting up traps and identifying BLH can be found in the article, Beet Leafhopper Monitoring with Yellow Sticky Cards.

Treatment thresholds based on BLH numbers on traps have not been established, but we know that the risk of infection increases as BLH populations become large. If the numbers on traps build up to 40 or more BLH per week, then it is probably time to be concerned. A typical weekly catch during peak BLH activity is 100. Eliminating weed hosts (wild mustards, Russian thistle, kochia) in areas surrounding potato fields is an important cultural management approach for BLH. Potato growers may also select cultivars that are less susceptible to purple top (Ranger, Umatilla, and Norkotah are considered highly susceptible; Russet Burbank is susceptible; and Alturas and Shepody are moderately susceptible).

A number of insecticides are labeled for use on potatoes to control leafhoppers. Systemic at-planting insecticides, especially those with longer residual activity applied at the maximum allowed rate, have been shown to provide some early season control of BLH. Results may vary depending on the product used, application rate, soil and environmental conditions, and insect pressure. Foliar insecticides may also be used to control BLH. These are usually applied in May, June, and sometimes July. Insecticides with long residual activity (10-14 days) are preferred. If you apply a non-systemic insecticide, it may be necessary to shorten the application interval during periods of rapid plant growth to ensure adequate plant coverage. Remember to always read and follow instructions on the pesticide label. For more information about managing BLH, visit IPM Guidelines for Insects and Mites in ID, OR, and WA Potatoes and the PNW Insect Management Handbook.

POTATO PSYLLIDS 

The number of potato psyllids being found in Columbia Basin potato fields has continued to increase. This week, we collected 67 adult potato psyllids on sticky cards (1-5 per card) in sampling network fields across the Basin. Another 144 psyllids (1-32 per card) were brought to us by crop advisers. We will be testing these psyllids to determine if they are carrying Liberibacter (Lso), the bacterium that causes zebra chip. Only a few potato psyllids in the Columbia Basin this season have been reported to carry Lso, but it is enough to cause concern. Widespread damage is possible even when infection levels in psyllid populations are low. So far, no major zebra chip outbreaks have been reported, but a few plants with zebra chip have been confirmed in a couple of fields near the Tri-Cities and one field north of Basin City. It takes about 3 weeks for the symptoms to show up, so by the time you see symptoms the psyllids will have had some time to spread the infection to more plants. Most potato growers in the region are applying insecticides to manage potato psyllids and limit the spread of zebra chip. If you find one or more psyllids, it is recommended that you apply an insecticide to control them. If you find potato psyllids, please let us know by sending an email to cwohleb@wsu.edu. We can help you submit psyllids for Lso testing.

Potato psyllids are important pests mostly because they can transmit a bacterium (Candidatus Liberibacter solanacearum) to potatoes that causes zebra chip disease (ZC). This disease reduces both yield and tuber quality and has lead to serious economic losses in some regions. ZC was first detected in potato fields in the Columbia Basin in 2011, and occurred again in 2012.

Yellow sticky cards are recommended for detecting psyllid migration into an area. The cards should be placed inside the field, near the field edge, and just above the canopy level. It is best to have five or more yellow sticky cards around the field. Another method for sampling adult psyllids is to use an inverted leaf blower with a mesh net secured to the end of the cylinder (see photo on the sidebar). This method is better for detecting low population densities than the sticky cards. Operate the machine (in vacuum mode) above the potato plants for at least 5 minutes, 5-10 feet from the edge of the field, and then carefully remove the net from the end of the cylinder. It helps to transfer the insects from the net to a plastic bag that you can seal, and then look for the tiny winged adults. If you place the bag in the freezer for a while, you can slow the buzzing insects down which will make it easier to scan the bag. Other life stages of the psyllid may be found by collecting several leaves (mid-plant) from the outer rows of the field, and then scanning the underside (with a hand-lens) for the tiny nymphs and eggs. It is also recommended to scout for psyllids in cull piles and volunteer potatoes. For more information about psyllids, including insect identification, monitoring, and control recommendations, read Biology and Management of Potato Psyllid in Pacific Northwest Potatoes and Potato Psyllid Vector of Zebra Chip Disease in the Pacific Northwest.

APHIDS 

Aphid numbers are increasing, especially in the lower Columbia Basin. Aphids were detected in 61% of the potato fields we sampled this week. Wingless green peach aphids were found in 52% of the fields and they averaged 0.8 aphids per plant. One field had as many as 8 aphids per plant. Keep monitoring your fields for aphids, because their numbers can really increase as the season progresses. It is not unusual to see big aphid outbreaks as we move to the latter part of the growing season. Go to the pest data mapping section below to see all of the aphid counts for this week.

Aphids are important pests because they transmit several important potato viruses, especially potato leafroll virus (PLRV) and potato virus Y (PVY). Green peach aphids are the most important vector of PLRV, which has caused substantial yield and tuber quality losses in the Columbia Basin. PLRV causes net necrosis in some cultivars, an unacceptable tuber defect in processing potatoes. PVY can also result in significant yield losses, and some strains cause tuber defects. 

Potato growers should monitor fields for aphids at least once a week, because early recognition and control of aphids is the best tactic in limiting spread of potato viruses. Current recommendations are to treat long-season storage potatoes as soon as wingless aphids are detected. Low tolerances have been established because even a low incidence of seed borne PVY and PLRV can spread rapidly if aphids go unchecked.

POTATO TUBERWORM (PTW) 

Moths were found at 12 locations in the Columbia Basin of Washington this week; at locations from north of Warden to fields near the WA/OR border. The moth counts ranged from 1 to 59 PTW moths per trap. Go to the pest data mapping section below to see all of the PTW moth trap counts for this week.

Potato tuberworm (PTW) was first recognized as an important pest of potatoes in the southern Columbia Basin in 2003. PTW larvae feed on tubers causing damage that renders them unmarketable. Potato growers with fields south of Connell, WA are recommended to pay close attention to regional trapping data, and should deploy pheromone traps. Infestations of PTW are highly localized, and it is risky to conclude too much from traps that may be several miles away. Information about setting up traps and identifying PTW moths can be found in the article, Tuberworm Monitoring with Pheromone Traps. Trap counts from mid-season to harvest are particularly important to watch. Pre-harvest control measures may be warranted in fields where PTW moths in pheromone traps are found to be increasing every week, especially in August-October.

SPIDER MITES

We found spider mites in 13% of the potato fields we visited this week. Sampling for mites requires close visual inspection because they are tiny. It helps to shake plants over a white paper and then look for the tiny moving dots. If you plan to apply a miticide, then apply it early because none of the registered miticide products provide full control once populations reach outbreak levels. A well-times application is made when mite populations reach 2 mites per leaf, which is close to the detection limit for the pest. Include a surfactant to improve coverage (refer to the miticide product label for specific information). In most cases, a single, well-timed application will control mites. More information can be found in IPM Guidelines for Insects and Mites in ID, OR, and WA Potatoes.

BENEFICIAL INSECTS

This week, we found big-eyed bugs in 42% of the fields we sampled, and damsel bugs in 26% of the fields. We also observed quite a few minute pirate bugs. All of these are “good guys” that prey on insect pests.

Previous 2013 reports - click here


Pest Data Mapping

Click on the map to view insect population data (http://www.nwpotatoresearch.com/IPM-Home.cfm).

 

Click map

BLH Weekly Trapping Data

Click graph for larger image

Click to view larger image

Useful links

This project is sponsored by the Washington State Potato Commission.

Quick links


Pest alerts via email!

Subscribe to receive weekly pest alerts via e-mail by sending an e-mail to Carrie Wohleb (cwohleb@wsu.edu).

Trapping supplies

The Washington State Potato Commission is offering free supplies to Washington growers for trapping leafhoppers and tuberworm moths. To receive supplies for trapping these insects, simply call the commission office (509) 765-8845 or send an e-mail to ajensen@potatoes.com

Beet leafhopper (photo by Andy Jensen, WA State Potato Commission)
Beet leafhopper
Potato tuberworm moth (photo by Andy Jensen, WA State Potato Commission)
Potato tuberworm moth
Green peach aphid (photo by Andy Jensen, WA State Potato Commission)
Green peach aphid
Potato aphid (photo by Andy Jensen, WA State Potato Commission)
Potato aphid
Potato psyllid
Potato psyllid
Psyllid sampling with a leaf blower/vacuum
Psyllid sampling with a leaf blower/vacuum
Bucket sampling for aphids
Aphid sampling with a bucket

For more information about the potato insect pest survey contact:

Carrie H. Wohleb, Ph.D.
Potato and Vegetable Production Systems
Washington State University Extension, Grant/Adams Area
Courthouse, PO Box 37
35 C Street NW
Ephrata, WA 98823
phone 509.754.2011 ext. 413
FAX 509.754.0163 cwohleb@wsu.edu

Potatoes at WSU, PO Box 646414, Washington State University, Pullman WA 99164-6414, 509-335-9502, Contact Us