Spring 2015 Sustainable Management Strategies for Control of Flea Beetles Gadi V.P. Reddy, Superintendent & Associate Professor of Entomology/Insect Ecology, Western Triangle Agricultural Research Center, Conrad, MT The crucifer flea beetle, Phyllotreta cruciferae leads to concentrations of beetles and injury (Goeze), has lately emerged as a serious pest along field margins. of canola in Montana. The adult beetles The Western Triangle Agricultural Research feed on canola leaves, causing numerous Center (WTARC) near Conrad, Montana, small holes that stunt growth and reduce carried out field trials during 2013 at two yield (Figure 1). In 2013, injury to canola locations. The objectives were to determine seedlings was high (nearly 80%) in many nominal threshold levels for flea beetle on parts of Montana. This demonstrates that canola. The results indicated that a threshold when flea beetles emerge in large numbers of 15-20% leaf area injury is recommended for they can quickly put an end to a young an insecticidal treatment in order to reduce the spring canola crop. Each year, yield losses number of chemical applications and also reduce due to flea beetle damage in the Northern the possibility of selecting for resistance in flea Great Pains have been estimated to be tens beetles in Montana. However, in North Dakota, of millions of dollars. to protect the crop from yield losses, these Flea beetles have a single generation insecticides are regularly applied at an economic per year and overwinter as adults in the threshold of 25% feeding injury to cotyledons INSIDE: leaf litter of shelterbelts or grassy areas; and first true leaves. however beetles are rarely found in canola Insecticide application is the main tactic for Sustainable Management Strategies stubble. Beetles emerge when temperatures flea beetle management on canola, and the for Control of Flea Beetles ...............1 approach 57°F in early spring, proceed majority of canola acreages in North America Collecting and Submitting to feed on canola and weeds such as wild are treated with insecticides. Classically, Plant Disease, Insect and Plant mustard and other brassicas and then insecticide applications are made targeting adults Identification Samples .......................2 move into newly sown canola as plants in early spring when the canola crop is at the Bulbous Bluegrass ...........................4 emerge. Depending on temperature, it seedling stage, which is the most susceptible to may take up to three weeks for all adults Pest Management Toolkit ...............5 to leave their overwintering sites. Adults Respiratory Protection of Increasing feed on cotyledons and developing leaves Concern for Montana Pesticide and stems of seedlings, leading to loss of Applicators ......................................6 photosynthetic capability and finally plant Meet Your Specialist: death (Figure 2). Feeding starts within Emily Glunk ...................................7 the first two weeks after beetle emergence and produces a shot-hole appearance Ask an Expert .................................8 and necrosis. Warm, dry, calm weather encourages flea beetle flight and feeding throughout the field, while at the same time slowing canola growth. In contrast, cool, rainy, and windy conditions decrease flight FIGURE 1. Crucifer flea beetle, Phyllotreta activity, but flea beetles walk or hop which cruciferae. Enlarged to show detail. 2 (flea beetles, continued from page 1) flea beetle damage. In the Golden Triangle areas in Montana, canola growers traditionally Collecting and Submitting Plant Disease, use seed treatments. Neonicotinoid Insect and Plant Identification Samples for insecticides, applied either as seed treatment or foliar sprays are used as the main Diagnosis to the Schutter Diagnostic Laboratory approach for the management of flea beetles. Eva Grimme, Plant Pathology Diagnostician, Schutter Diagnostic Laboratory; Mary Insecticidal seed treatments with imidacloprid Burrows, Extension Plant Pathologist; and Laurie Kerzicnik, Insect Diagnostician are used throughout the Northern Great Plains to systemically protect canola seedlings Plant diagnosticians at Montana State Keep some soil around the root ball and off from flea beetle attack. Other approaches, University in the Schutter Diagnostic foliage. Wrap the plant sample in plastic including repeated applications of carbaryl, Laboratory are available to identify any and secure with a rubber band around the are often needed in order to keep flea beetles problems that affect plants in the landscape. base of the plant (Figure 3). This prevents below economic injury levels; additionally, Accurate identification of plant disorders the soil from damaging the leaves during foliar spray of insecticides, i.e. deltamethrin and pests are the foundation for integrated shipping. Loosely enclose the foliage in or bifenthrin, are also used to prevent flea pest management. A good quality sample plastic or paper. Do not add water. beetles from causing significant feeding injury. and as much information as you can However, due to environmental concerns Send a sample so that we could plant it provide on the history of the problem is (i.e. impact on pollinators and natural when it arrived and it would survive. important for accurate, fast diagnosis and enemies from the frequent and heavy use of Package samples in crush-proof containers. appropriate recommendations. To expedite chemical insecticides), more environmentally- Never send leaves in a flat paper envelope – Dry weather and weed management identification and recommendations, compatible tactics are desirable for sustainable the post office machinery causes extensive Fabian Menalled, MSU Crop Weeds Specialist please follow the following guidelines. management of this pest. damage, and the tissue rots or dries out in Submission instructions, forms, and more shipping. If you are planning to mechanically manage The field experiments conducted by information can be found at our website, your weeds, remember that tillage reduces soil WTARC during 2013 indicated that http://diagnostics.montana.edu/. You can Include photographs illustrating the moisture. When soils are dry, tillage could combined use of entomopathogens drop samples off with your local county problem if possible. Make sure photos result in seedbed desiccation and reduced (fungi), Beauveria bassiana (2.4 g/liter) Extension agent or submit them to the lab are in focus, and include your name crop establishment. The risk of soil erosion and Metarhizium brunneum (5 g/liter) directly. Your county agent is a good place and contact information with sample significantly increases in dry conditions. You is more effective in reducing feeding to start – they are familiar with many of the submissions. Email the photographs to can minimize moisture losses by applying injuries and improving yield levels when plant disorders in the community, and may [email protected]. shallow tillage and using a harrow to fill in compared to chemical control and other be able to identify your problem right away. Always include background information. and seal the ground. In most cases, adopting treatment strategies. This indicates that Plant problems are often influenced by Plant Disease Specimens minimum tillage or no-tillage techniques may entomopathogenic fungi are effective against many different factors, so include as much be the best solution to conserve soil moisture; flea beetles and may serve as alternatives to Send sufficient plant material. Examine information as possible: plant and variety, however care should be taken to reduce the conventional insecticides or seed treatments the entire plant for symptoms and collect location (greenhouse, field, windbreak, proliferation of perennial weed species. in managing this pest. samples that show various stages of the home garden, etc.), irrigation practices Drought not only complicates weed problem. Include a healthy plant or plant (type of system, frequency, amount management, but also increases crop part for comparison. Send enough plant applied), history (age, size, amendments, susceptibility to pre- and post-emergence material so that an identification can be fertilizer, etc.), pesticides used with names, herbicides. Dry weather reduces microbial made. Whenever it is practical, include rates, and dates, weather conditions, and chemical degradation of soil-applied roots or the entire plant or clump of pattern of symptoms on the plant and herbicides increasing carryover injuries. If plants. If that is not possible, include a surrounding plants, previous problems you applied a residual herbicide last fall, branch or send a twig. Detached leaves or in this location. In-depth background pay special attention to carryover problems. parts of leaves are seldom useful. information will help the diagnostician to Drought-stressed crops are more susceptible to Avoid sending dead plants or plant parts identify the problem and is essential for post-emergence herbicides, and the combined since they are not useful for accurate timely management recommendations. effect of herbicide injury and drought may FIGURE 2. Damage to canola leaves caused diagnosis. Do not ship on Fridays. Samples can rot, by flea beetles. reduce crop yield. Keep samples as fresh as possible until bake or freeze over the weekend. If we are lucky we won’t see a drought you can ship them. Avoid exposing the during the 2015 growing season, and sample to direct sunlight and refrigerate if you won’t need to be concerned with the possible.