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Squash Vine Borer

By Dr. Raymond Cloyd

We have received inquiries regarding cucumber and squash plants wilting and collapsing, and a recent visit to the Manhattan Community Garden (Manhattan, KS) provided evidence that the larvae of the squash vine borer (Melittia cucurbitae) are indeed active inside plants. Squash vine borers feed on squash, pumpkin, cucumber, and muskmelon.

Adults are “clear wing” moths 5/8 inches long. The front wings are covered with scales whereas the hind wings are transparent because they do not have scales. Hind wings have red-brown hairs along the edges. The body is orange-red, with gray bands and three black markings along with orange-red hairs on the abdomen (Figure 1).

Figure 1: Squash vine borer adult
Figure 1: Squash vine borer adult

Moths are active during the day with females depositing eggs on the stem near the soil level or on stems or petioles when plants begin to flower. The eggs are red-brown, flattened, 1/30 inches in diameter, and are typically located at the base of plants (Figure 2).

Figure 2: Squash vine borer eggs located at base of plant
Figure 2: Squash vine borer eggs located at base of plant

A single female is capable of producing up to 200 eggs. Larvae that hatch from eggs are white, with a dark head capsule. Young larvae are 1/4 to 3/4 inches in length and taper toward the end of the abdomen (Figure 3).

Figure 3: Young larva of squash vine borer
Figure 3: Young larva of squash vine borer

Mature or fully-grown larvae are 1.0 to 1.5 inches long (Figure 4).

Figure 4: Mature larva of squash vine borer larval feeding
Figure 4: Mature larva of squash vine borer larval feeding

Larvae that hatch from eggs immediately tunnel into the base of plants. The larvae feed for 30 days in the plant stem, and increase in size as they mature. Typically there is only one larva per stem; however, multiple larvae may be present in a single tunnel in the stem. Mature larvae leave plants and burrow into the soil to pupate by constructing brown, silkened cocoons in which they overwinter. Squash vine borer overwinters as a mature larva in the cocoon that is located 1.0 to 2.0 inches in the soil. In early spring, the adult (moth) emerges from the soil. Squash vine borer has one generation in Kansas.

At this point, squash vine borer larvae are feeding within the internal vascular tissues inhibiting the plant’s ability to take-up water and nutrients; consequently, resulting in sudden wilting of vines and plant collapse (Figure 5).

Figure 5: Plants wilting due to squash vine borer larval feeding
Figure 5: Plants wilting due to squash vine borer larval feeding

Once the larvae are inside the plant, there is little that can be done to control them or prevent damage. The tunnels inside infested plants are packed with moistened frass (fecal matter) (Figure 6).

Figure 6: Moistened frass or fecal matter inside infested plant stem
Figure 6: Moistened frass or fecal matter inside infested plant stem

Yellow-green sawdust-like frass can also be found around feeding sites at the base of vines or plants (Figure 7)

Figure 7: Frass or fecal matter near tunnel entrance of squash vine borer larvae
Figure 7: Frass or fecal matter near tunnel entrance of squash vine borer larvae

,which will be a direct indication that larvae have entered the plant.

Since the larvae are feeding inside the plant there is not much that can be done to kill the larvae; however, there are number of plant protection strategies that can be implemented during the remainder of the growing season, including: sanitation and physical control.

Sanitation: remove and dispose of all wilted plants before the larvae leave and enter the soil. Discard all plant debris such as vines and fruits after harvest.

Physical control: rototilling in fall or spring will directly kill squash vine borer pupae or bring the pupae to the soil surface where they are exposed to cold weather or predation by birds. In addition, the process of deep plowing will bury the pupae deeper in the soil profile thus inhibiting adult emergence. Another technique that may have limited use in large plantings but may be feasible for smaller plantings is to locate infested stems and vines, create slits at the base of the plant, and then use tweezers to remove and destroy the larvae inside. The plant base should then be covered with moist soil, which stimulates the production of secondary vines and/or root growth; thus helping the plant to re-establish.

There is a new up-dated extension publication on squash vine borer (MF3309) that contains current information on plant protection with images of the insect (both adult and larva) and plant damage. You can download a PDF from the following website:

http://www.bookstore.ksre.ksu.edu/pubs/MF3309.pdf

Japanese Beetles are Back!

— by Dr. Raymond Cloyd

Japanese beetle adults are out in full-force in certain regions of Kansas feeding on one of their favorite host plants…roses. The means of dealing with the adult stage of this insect pest are limited, however, and have been for many years, with the use of insecticides being the primary plant protection strategy. Japanese beetle, Popillia japonica is native to Japan and was first reported in the United States in 1916 in the state of New Jersey. Since then, Japanese beetles have spread throughout the country from Maine to Georgia with permanent establishments in nearly every state east of the Mississippi River and several western states west of the Mississippi River. Japanese beetles are established in eastern and central portions of Kansas and are slowly moving further west. The adult is one of the most destructive insect pests of horticultural plants in both landscapes and gardens. The larvae or grub is a major turfgrass pest in home lawns, commercial settings, and golf courses.

Japanese beetle adults are 9/16 inches long and metallic green with coppery-brown wing covers (Figure 1).

Fig 1: Close-up of Japanese beetle adult.
Fig 1: Close-up of Japanese beetle adult.

There are approximately 14 tufts of white hair present along the median of the abdomen (Figure 2).

Fig 2: Japanese beetle adult. Note tufts of white hairs on median of abdomen.
Fig 2: Japanese beetle adult. Note tufts of white hairs on median of abdomen.

Adult Japanese beetles emerge from the soil and live from 30 to 45 days feeding on plants over a four-to-six-week period. They feed on many ornamental plants including trees, shrubs, vines, herbaceous annual and perennials, and of course—roses. Plant placement in the landscape and volatiles emitted by plants are factors that influence adult acceptance. Furthermore, Japanese beetle adults produce aggregation pheromones that attract individuals (both males and females) to the same feeding location. Adults may fly up to five miles to locate a feeding site; however, they tend to fly only short distances to feed and lay eggs.

Japanese beetle adults feed through the upper leaf surface (epidermis) and leaf center (mesophyll), leaving the lower epidermis intact. They usually avoid feeding on tissue between leaf veins, resulting in leaves appearing lace-like or skeletonized (Figure 3).

Fig 3: Japanese beetle adult feeding damage.
Fig 3: Japanese beetle adult feeding damage.

Adults are most active during warm days, feeding on plants that are exposed to sunlight throughout the day, which is likely why roses are a susceptible host plant because they require at least six hours of direct sunlight. Japanese beetle adults also start feeding at the top of plants, migrating downward after depleting food sources. Japanese beetle adults aggregate in masses on rose flowers (Figure 4).

Fig 4: Japanese beetle adults aggregating on rose flower.
Fig 4: Japanese beetle adults aggregating on rose flower.

Although adult beetles feed primarily on flowers, they will also feed on leaves (Figure 5).

Fig 5: Japanese beetle adults feeding on leaves.
Fig 5: Japanese beetle adults feeding on leaves.

Japanese beetle adults chew holes in flower buds, which prevent flowers from opening or cause petals to fall prematurely. Moreover, adults will consume entire rose petals, and feed on the pollen of fully-opened flowers.

Japanese beetle adult management involves implementing a variety of plant protection strategies, including: cultural, physical, and insecticidal. Cultural involves maintaining healthy roses through proper irrigation, fertility, mulching, and pruning, which are important in minimizing any type of stress; thus possibly decreasing susceptibility. Also, removing weeds such as smartweed (Polygonum spp.) that are attractive to Japanese beetle adults will at least alleviate infestations. Physical is associated with hand-picking or collecting Japanese beetle adults from roses before populations are extensive. The appropriate time to hand-pick or collect adult beetles is in the morning when ambient air temperatures are typically “cooler.” Adults can be easily collected by placing a wide-mouthed jar or bucket containing rubbing alcohol (70% isopropyl alcohol) or soapy water underneath each adult, and then touching them. Adults that are disturbed fold their legs perpendicular to the body, and fall into the liquid and are subsequently killed. This procedure, when conducted daily or every-other-day, particularly after adults emerge, may substantially reduce plant damage. The use of Japanese beetle traps is not recommended since the floral lure and synthetically-derived sex pheromone may attract more adult beetles into an area than would “normally” occur. Adult beetles may also feed on roses before reaching the traps, which increases potential damage.

Spray applications of contact insecticides will kill Japanese beetle adults. Repeat applications will be required; especially when populations are excessive. Furthermore, thorough coverage of all plant parts will increase effectiveness of the application. The insecticide carbaryl (Sevin) and several pyrethroid-based insecticides including those containing bifenthrin or cyfluthrin as the active ingredient may be used to suppress Japanese beetle adult populations. However, since most of these insecticides are also directly harmful to many natural enemies (parasitoids and predators) their continual use may lead to secondary pest outbreaks of other pests including the twospotted spider mite (Tetranychus urticae). Moreover, these insecticides are directly harmful to pollinators (honey bees and bumble bees). Therefore, applications should be conducted in the early morning or late evening when pollinators are less active. In general, systemic insecticides, are not effective because Japanese beetle adults have to feed on leaves and consume lethal concentrations of the active ingredient. If extensive populations are present, then damage to plants may still occur.

The battle or war against Japanese beetle adults requires patience, persistence, and diligence in order to prevent adults from causing substantial damage to roses and other susceptible plants.

 

For more information on Japanese beetle and other pests of roses consult the following publication:

Compendium of Rose Diseases and Pests (second edition). 2007. APS Press. The American Phytopathological Society, St. Paul, MN.

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