Tag: pest

Allium leaf miner

Emily Zobel on
Adult allium leaf miners.

Allium leaf miner Phytomyza gymnostoma is a pest on chives, scallions, garlic, onions, and leeks. Overwinter ALM across the Mid-Atlantic will be emerging soon. Start scouting for ovipositor markings made by female ALM over the next few weeks on food and ornamental Allium crops. These markers will be neat rows of white spots descending from the upper tips of allium leaves. These marks will be typically be seen on the tallest leaves first. ALM Larvae mine leaves and moves towards and into bulbs and leaf sheathes. The leaf punctures and mines serve as entry routes for bacterial and fungal pathogens.

Spring crops are usually not as hard-hit as fall crops, especially when looking at leeks, but this pest has steadily increased its geographical range each year and its damage potential. If you had some infestation last year, you will especially want to look for this pest’s signs.

Yellow sticky cards or yellow plastic bowls containing soapy water can be used for monitoring but are not affected control independently. 

 

Onion leaf blades showing round white dots made by female Allium leaf miners. Photo by Jerry Brust

 

Cultural Control: Covering plants in February, prior to the emergence of adults, and keeping plants covered during spring emergence, can be used to exclude the pest. Avoiding the adult oviposition period by delaying planting (after mid-May we think) has also been suggested to reduce infestation rates. Covering fall plantings during the 2nd generation flight can be effective. Growing leeks as far as possible from chives has been suggested. Organic

 

Chemical Control: Azadirachtin (Aza-Direct or other formulations) or spinosad (Entrust or other formulations) follow label instructions for leaf miner.

Synthetic Chemical Control: Systemic and contact insecticides can be effective. EPA registrations vary, however, among Allium crops. Check labels to ensure the crop is listed, and for rates and days-to-harvest intervals. Options that may be effective include cyromazine (Triguard), dinotefuran (Scorpion), spinetoram (Radiant), lambda-cyhalothrin (Warrior II or other formulations), and abamectin (Agri-Mek or other formulations).

Asparagus Beetle IPM

Emily Zobel on

There are two beetle pests that feed on asparagus, the common or striped asparagus beetle (Crioceris asparagi) and the spotted asparagus beetle (Crioceris duodecimpunctata). Feeding on the spears results in scarring, browning, and hooked tips render the crop unmarketable. While both beetles can damage the emerging spears, the common asparagus beetle larvae and adults will also feed on the ferns, which can reduce the plant’s ability to build resources for a strong crop the following spring.

 

Fig 1. Adult Asparagus Beetle Photo by Clemson University – USDA Cooperative Extension Slide Series, Bugwood.org
Fig 2. Adult spotted asparagus beetle.
Photo by Whitney Cranshaw, Colorado State University, Bugwood.org

Adults: Adult beetles are about ⅓ inch in length. The adult common asparagus beetle is blue-blackish with six cream-colored square-shaped spots on its back (Fig 1). Adult spotted asparagus beetles are reddish-orange with twelve black spots on their back (Fig 2). Both the beetles overwinter as adults.

Fig 3. Asparagus Beetle Eggs. Photo by Ward Upham, Kansas State University, Bugwood.org

Eggs: Eggs take about a week to hatch. They are small, cylindrical, and dark-colored. The asparagus beetle lays eggs on the spear at a 90-degree angle in rows of 3 to 8 eggs (Fig 3.), while the spotted asparagus beetle oviposits eggs singularly on the fern.

 

Common Asparagus Beetle Larvae.
Fig 4. Common Asparagus Beetle Larvae. Photo by Clemson University – USDA Cooperative Extension Slide Series , Bugwood.org

Larvae: The larvae of both species are light gray with visible heads and legs. The common asparagus beetle larvae have blackheads (Fig 4.), while the spotted asparagus beetle larvae have an orange head. Larval feeding lasts for 10-14 days. Asparagus beetle larvae feed on the spear, while spotted asparagus beetles will burrow into the berry. Mature larvae crawl to the ground and burrow within the soil to pupate.

Scouting: Scouting should start at the end of April – early May or just after asparagus plants emerge and continue for the rest of the growing season. Check 10 plants in 5-10 different locations in a field, best on a warm, sunny afternoon when beetles will be most active. Treatment may be justified if 10% of spears are infested with beetles or 1-2% have eggs. 

Cultural Controls & Prevention:

  • During harvest, harvest all spears every day to reduce the number of stems where eggs will survive for long enough to hatch.
  • Allow plants in one area to develop ferns so as to act as a trap crop. These plants can then be sprayed selectively.
  • Maintain a clean environment in asparagus fields in the fall to force adults to overwinter in field edges where natural predators reside. 
  • Destruction of crop residues will eliminate overwintering sites for asparagus beetles.  
  • The most important natural enemy of the common asparagus beetle is a tiny parasitic wasp (Tetrastichus asparagi) that attacks the egg stage. These parasitoids lay their own eggs inside the beetle eggs. The immature wasps grow inside the beetle larvae, killing them when they pupate. Studies have found >50% of eggs were killed by parasitoid feeding, and half of the surviving larvae were parasitized. Providing a nearby nectar source such as umbelliferous flowers may enhance wasp populations.

Chemical Control 

  • Organic options on spears include Surround WP as a repellent, EC5.0, or products containing capsaicin (check for certification status).
  • If possible, spot spray along edges of planting where overwintering adults colonize the field and/or band insecticide over the row to help spare natural enemies. Use selective insecticides on ferns.
  • Daily harvest of asparagus makes chemical treatment difficult. 1 dh products are available and can be used immediately after picking to allow harvest the following day (see the Mid-Atlantic Commercial Vegetable Production Recommendations for current recommendations)

 

E. Zobel

Allium (Onion) Leafminer

Emily Zobel on

Allium leafminer (ALM), Phytomyza gymnostoma (Diptera: Agromyzidae), is an invasive leaf-mining fly from Poland that was first detected in Pennsylvania in 2015. They overwinter as pupae in plant tissue or surrounding soil. Adults emerge mid-March throughout April (250°Degree Days with a minimum temperature threshold of 3.5°C.). The adults are small (~ 3 mm) long grey or black flies with a distinctive yellow or orange area on the top and front of head and legs have distinctive yellow “knees” (Fig.1, Fig 2). The larvae are white maggots, headless, and around ~ 8 mm long at their final instar.  The pupa are dark brown, ~3.5 mm long.

Adult allium leafminer
Figure 1. Adult allium leafminers. Photo by Lawrence Barringer, Pennsylvania Department of Agriculture, Bugwood.org
Figure 1. Allium leafminer on scallion leaf.
Figure 2. Allium leafminer on scallion leaf. Photo: Brandon Lingbeek, Penn State

 Adults will mate lay eggs inside the leaves of Allium species, creating a row of several small round white dots (made by the female’s ovipositor) on the top half of the leaf blades (Fig.3). Larvae mine leaves and move towards and into bulbs and leaf sheathes. Damage from Allium leafminer can also cause the plant to exhibit curly, wavy or distorted leaves. Both the leaf punctures and mines serve as entry routes for bacterial and fungal pathogens. The larvae may move into the soil to pupate. These pupae undergo a diapause period which lasts throughout the summer, and will emerge as adults in the autumn (September / October). 

Allium leafminer
Figure 3. Oviposition and feeding damage by Allium leafminer. Photo by Lawrence Barringer, Pennsylvania Department of Agriculture, Bugwood.org

 While spring crops are usually not as hard hit as fall crops, this pest has been steadily increasing its geographical range each year and its damage potential. Fields that had pressure last year should be scouted for feeding damage this year.  Yellow sticky cards or yellow plastic bowls containing soapy water can be used for monitoring this pest. You can reduce infestation rates by rotating fields, growing leeks as far as possible from chives, and delaying the planting of spring allium crops. Growing allium crops on reflective mulch has reduced the severity of allium leafminer damage in research trials in New York. Placing row covers over allium crops during the period flies and keeping plants covered during the 3-4 weeks of emergence will exclude the pest. Larvae and pupa tend to be found in the outermost layers of leaves from leek and scallion, so the hand removal of these layer will often create a blemish-free product.

Several systemic and contact insecticides are approved for this pest, but EPA registrations vary among Allium crops. When using chemical control, check labels to ensure the crop is listed and for rates and days-to-harvest intervals. Always read and follow the label. The label is the Law.  

 For chemical recommendations, see the 2020-2021 Mid-Atlantic Commercial Vegetable Production Recommendation Guide: https://extension.umd.edu/mdvegetables/2020-2021-mid-atlantic-commercial-vegetable-production/commodity-recommendations 

 Azadirachtin (Aza-Direct or other formulations) or spinosad (Entrust or other formulations) are options for organic chemical control.