Posts Tagged ‘seed corn maggot’

Seedcorn Maggot and Cabbage Maggot Damage Possible in the Next Few Weeks

Thursday, April 26th, 2012

Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu

The unusually warm and dry spring we have had up to now has led many growers to transplant some of their melon and other vegetable crops early. The cool wet weather we have had in the last few days will make some of these fields vulnerable to seed corn maggots Delia platura (SCM) or less commonly found in cucurbit fields, cabbage maggots, Delia radicum (CM). Both species overwinter in the soil as a maggot inside a brown case. In March and April small, grayish-brown flies emerge. Adult flies are most active from 10 a.m. to 2 p.m. and are inactive at night, in strong winds and when temperatures are below 50o F or above 80o F. Female cabbage maggot flies seek out and lay eggs on the lower portions of stems of young host seedlings or in nearby cracks in the soil. Within a few days the eggs hatch and the tiny maggots burrow down to the roots and begin feeding. SCM eggs are oviposited in soils with decaying plant material or manure. The adults are also attracted to the organic media around the roots of transplants and germinating seeds. That is why fields that have been fumigated can still have problems with SCM. Maggots will move into small stems and move up the plant causing a swelling of the stem just above ground level, while also causing root collapse and decay. If these stems are split you will usually find the white cylindrical larvae (Photos 1, 2 and 3).

 

Photos 1, 2 and 3. Swollen stem of cucurbit plant with collapsed rotting roots. When stem is cut open the white maggots often can be found.

The adult flies are often found dead, stuck to vegetation during periods of warm wet weather (like we had in early April). These flies have been infected by a fungus, Entomophthora sp. These infected flies usually will be found at the top of a tall object in the field such as a grass seed head or a wire field-flag (Photo 4). Just before the fungus kills them they cement their body via their mouthparts to the tall object and die. If you look closely you’ll see the body is filled with the white fungus that has ruptured between the segments (Photo 5). Being on a tall object allows the spores of the fungus to move longer distances and infect more flies than if the fly had died on the ground. Even though we have had a dry spring, I still have seen many fungus infected dead flies this year. Unfortunately, the infection rate is not enough to reduce the SCM population and stop infestations.

Soil temperatures two inches deep in the planting hole that are at or above 70o F reduce SCM egg laying and larval survival. If soil temperatures are above 70o F at planting but fall below this level for several days in a row (which they have just done), SCM adults will begin to oviposit eggs at the base of transplants. When wilted transplants are inspected in the field, maggots are often not found (they have already pupated), but their tell-tale damage can be seen as a hollowed out stem or root held together by a few strands of plant material. The use of treated seed or in-row banding of an insecticide gives some control of SCM, however, replacing dead transplants is the only solution after SCMs kill a plant. Once seed corn maggot damage is noticed, it is too late to apply control procedures. Thus, economic thresholds are not useful and all management options are preventative.

Photo 4. Two SCM flies killed by a fungus stuck to a wire field-flag via their mouthparts

Photo 5. Adult SCM killed by a fungus – white strands coming out of abdomen

Seed Corn Maggots Control in Field Corn

Friday, March 2nd, 2012

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

With the warm winter conditions, we have observed flies actively laying eggs earlier and for a longer period of time. Adult flies are active in temperatures down to the mid 40s so it very likely that maggot populations could be higher in early planted field corn. Conditions that favor egg laying activity include decaying cover crops, high organic matter, freshly plowed fields, and/or manure applications. Control options include commercial applied seed treatments, or soil insecticides. It should be noted that seed treatment labels indicate that they only provide early season protection of seedlings against injury from seed corn maggots.

Seed Corn Maggots Control in Spring Planted Vegetables

Friday, March 2nd, 2012

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

With the warm winter conditions, we have observed seed corn maggot flies actively laying eggs earlier and for a longer period of time. Adult flies are active in temperatures down to the mid 40s so it very likely that maggot populations could be higher in spring planted vegetables. Conditions that favor egg laying activity include decaying cover crops, high organic matter, freshly plowed fields, and/or manure applications. Spring planted vegetables susceptible to maggot damage include cole crops, melons, peas, snap beans, spinach, and sweet corn. Control options can include commercial applied seed treatments, or soil insecticides; however, not all options are available for all crops. As a reminder, seed treatment labels indicate that they provide only early season protection of seedlings against injury from seed corn maggots. Please refer to the labels as well as the DE Commercial Vegetable Production Recommendationshttp://ag.udel.edu/extension/vegprogram/publications.htm#vegrecs

Vegetable Crop Insects – April 8, 2011

Friday, April 8th, 2011

Seed Corn Maggots (SCM) Control in Spring Planted Vegetables
We continue to observe flies actively laying eggs in a number of situations including recently plowed fields, especially when a cover crop is plowed under or when manure was applied to a field. Spring planted vegetables susceptible to maggot damage include cole crops, melons, peas, snap beans, spinach, and sweet corn. Control options can include commercial applied seed treatments, or soil insecticides; however, not all options are available for all crops. Please refer to the labels as well as the DE Commercial Vegetable Production Recommendations.

Cabbage
As soon as plants are set in the field, begin scouting fields for imported cabbage worm and diamondback larvae. As a general guideline, a treatment is recommended if you find 5% of the plants infested with larvae.

Peas
Be sure to sample for pea aphids as soon as small seedlings emerge. On small plants, you should sample for aphids by counting the number of aphids on 10 plants in 10 locations throughout a field. On larger plants, take 10 sweeps in 10 locations. As a general guideline, a treatment is recommended if you find 5-10 aphids per plant or 50 or more aphids per sweep. In general, aphid development is favored by cool, dry weather which slows beneficial activity but is favorable for the development of aphids.

Sweet Corn Vigor

Thursday, May 20th, 2010

Gordon Johnson, Extension Fruit & Vegetable Specialist; gcjohn@udel.edu

Each year we see sweet corn fields with stand and plant vigor issues, especially in early planted fields. There can be many causes for stand loss and weak seedlings: surface compaction and crusting, birds, soil insects, cold soils that delay emergence, soil diseases affecting seeds or seedlings, wet soils, fertilizer injury, deep planting, and herbicide injury are just a few examples.

When checking sweet corn fields with vigor and stand problems, it is important to dig up seeds and affected plants and examine the seed remnants, roots, and mesocotyl (stem that pushes the seed leaf to emerge above the ground). Corn seedling survival and early vigor is directly tied to a healthy seed kernel and mesocotyl from planting through the six leaf stage. Any damage to the seed or mesocotyl during this period can lead to stunted or weak seedlings, and in severe cases, seedling death. This is because the corn seedling depends on the seed for food to grow for several weeks after emergence until sufficient leaf area has been produced and nodal roots have become established. The seed kernel provides the means for early roots to grow and these food reserves are also mobilized and transported through the mesocotyl to grow the first stalk and leaf tissue. The mesocotyl also serves to transport water and mineral nutrients from the seedling roots.

Sweet corn is more susceptible stand loss and poor vigor problems than field corn because the seed has less food reserves. Shrunken types (supersweet and sugary enhanced varieties) have even less stored food than “normal” types and therefore are more susceptible to stand problems.

I have looked at sweet corn fields with stand loss and vigor problems (uneven growth) over the years. Often, when digging up the seedlings and examining the seed remnants and mesocotyls, the kernels will be disintegrated and there will be darkening at the mesocotyl attachment. This means that the seeds will have deteriorated prematurely and therefore the full content of the food reserves in the seed were not available for seedling development leading to the stand and vigor issues. The question that needs to be answered is what caused the seed to deteriorate prematurely?

The answer of course will change from field to field. Seed deterioration and/or poor vigor seedlings can be due to diseases that cause seed rots, seedling blights and/or root rots. Fungal disease organisms such as Pythium, Fusarium, Rhizoctonia, Aspergillus, and Penicillium are common in soils and many can even be carried on seeds. Fungicide seed treatments are critical to control these diseases. Problems occur where seed treatments are not adequate, where disease organisms are at very high levels, or where soil conditions are too cold and seeds remain in the soil for extended periods before germination and emergence. The risk of seeding infection increases as germination and emergence is extended and protecting seed treatments dissipate.

Cold stress and cold soils is a common stress factor leading to poor stands. Often growers are pushing the limits and are planting sweet corn too early. While field corn will start to germinate at 50°F, many types of sweet corn need much warmer soils. This is especially true of supersweets and other shrunken types which perform best at soil temperatures 65°F or higher. Sweet corn germinates best at soil temperatures above 68°F. When soil temperatures are below 55°F, germination is greatly extended. Food nutrients are mobilized in the seed but are not being utilized rapidly by the plant. The seed then becomes a perfect food source for many soil microorganisms.

Soil insects can cause seed deterioration by feeding on seed contents and causing entrance wounds for disease organisms. Seed corn maggots and wireworms can feed on the seed directly causing stand losses. Grubs feed on seedling roots causing stunting. Wireworms and certain grubs will also feed on the mesocotyl causing seedlings to collapse. Sweet corn that takes more than 10 days to emerge is at great risk of injury due to insects as seed treatments dissipate. In fields with heavy infestations of soil insects seed treatments may not be adequate. Addition of manures or other organic matter sources just prior to early plantings can lead to heavy seed corn maggot populations that overwhelm seed treatments.

Stand issues are often related to the inherent poor vigor of sweet corn. Work with seed suppliers to obtain their best lots for early plantings with the largest seed sizes. Obtain varieties that perform better under cold stress.

The University of Delaware has two separate trials of processing sweet corn varieties from several seed companies that were planted in both early (April) and later (May). Results from these trials will be available later this year for future planning.

Seedcorn Maggot Damage in Early Planted Cucurbit Fields

Thursday, April 29th, 2010

Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu

There have been several reports throughout Maryland of early planted watermelon and cantaloupe fields with seedcorn maggot (SCM) damage. The damage to transplants is often thought to be just damping-off or some other soil disease, but growers need to split the stems of the plants to see if they contain any seedcorn maggots. Stems can contain 12-45 maggots. The stem often looks whole above ground level, but below ground the stem and roots are often shredded (Fig. 1). The seedcorn maggot is an early season pest of many different crops. Most of these crops are direct seeded, but transplants are also attacked. It is more of a problem during damp, cool periods and in fields with manure or decaying residue. This year has been perfect for the fly to cause damage as we had a very early warm up followed by a cool down. This caused growers to start earlier and it also caused more of the pest population to become active early.

The seedcorn maggot is a pale, yellowish-white maggot found burrowing into seeds or transplants. Full grown maggots are legless, about 1/4 inch long, cylindrical, narrow and tapered. Maggots lack heads and legs, but have small black mouth hooks in front (Fig. 2).

The seedcorn maggot spends the winter as a larva inside a puparium in the soil. When mature, maggots pupate and emerge in April and May, mate, and lay eggs on moist soil high in organic matter, near decaying vegetation or at the base of transplants. The adult, which resembles a small house fly, is a gray to brown fly about 1/5 inch long that can be seen flying over freshly worked soil or where manure has been spread.

Seedcorn maggot eggs hatch a few days after being laid, and small, white, tapered maggots begin to feed on and burrow into plants or seeds. The maggots usually feed for 2 to 3 weeks before pupating in the soil. Adults emerge from the pupal case in about 7 to 14 days, mate, and begin a new cycle. The entire life cycle is as quick as 21 days, resulting in 3 or more generations each year.

There are no rescue treatments for infested plants. Fumigation and soil insecticides do not do a very good job of reducing SCM infestations since the maggots attack the seedling just below soil level. Even the use of systemic insecticides does not completely control maggot infestation s if the weather is cool and damp. The best control is a warmed soil. My research has shown that when temperatures reach 71oF at a 4 inch depth under BLACK PLASTIC, flies will stop laying eggs and larvae do not survive well. Row covers over the newly set transplants will also work to keep flies from laying eggs in the transplants.

 

Figure. 1 Transplant damaged by seedcorn maggot

 

Figure. 2 Maggots inside split stem of cantaloupe transplant

Vegetable Crop Insects

Thursday, April 8th, 2010

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

Seed Corn Maggots (SCM) Control in Spring Planted Vegetables
We continue to observe flies actively laying eggs in a number of situations including recently plowed fields, especially when a cover crop is plowed under or when manure was applied to a field. Spring planted vegetables susceptible to maggot damage include cole crops, melons, peas, snap beans, spinach, and sweet corn. Control options can include commercial applied seed treatments, or soil insecticides; however, not all options are available for all crops. Please refer to the labels as well as the 2010 DE Commercial Vegetable Recommendations for control options.

Cabbage
As soon as plants are set in the field, begin scouting fields for imported cabbage worm and diamondback larvae. As a general guideline, a treatment is recommended if you find 5% of the plants infested with larvae.

Peas
Be sure to sample for pea aphids as soon as small seedlings emerge. On small plants, you should sample for aphids by counting the number of aphids on 10 plants in 10 locations throughout a field. On larger plants, take 10 sweeps in 10 locations. As a general guideline, a treatment is recommended if you find 5-10 aphids per plant or 50 or more aphids per sweep. In general, aphid development is favored by cool, dry weather which slows beneficial activity but is favorable for the development of aphids. Be sure to check labels for application restrictions during bloom.

Seed Corn Maggot (SCM) Control in Spring Planted Vegetables

Friday, April 3rd, 2009

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

We continue to observe seed corn maggot flies actively laying eggs in a number of situations including recently plowed fields, especially when a cover crop is plowed under or when manure was applied to a field. Spring planted vegetables susceptible to maggot damage include cole crops, melons, peas, snap beans, spinach, and sweet corn. Control options can include commercial applied seed treatments, or soil insecticides; however, not all options are available for all crops. The hopper box treatment Latitude (imidacloprid) is available in our area and is only labeled on sweet corn. Please refer to the labels as well as the 2009 Delaware Commercial Vegetable Production Recommendations.

Seed Corn Maggot in Melons

Friday, May 23rd, 2008

Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu

The recent very wet and cool temperatures we have had over the last two weeks have resulted in several fields of early planted cantaloupe and watermelon having seed corn maggot infestations. Seed corn maggots (SCM) overwinter in the soil as a maggot inside a brown case. In March and April small, grayish-brown flies emerge. Adult flies are most active from 10 a.m. – 2 p.m. and are inactive at night, in strong winds and when temperatures are below 50o F or above 80o F. Eggs are oviposited in soils with decaying plant material or manure. The adults are also attracted to the media around the roots of transplants and to germinating seeds. That is why fields that have been fumigated can still have problems with SCM. SCM flies are often found dead stuck to vegetation during periods of warm wet weather. These flies have been infected by a fungus, but the infection rate is rarely enough to reduce the SCM population and stop infestations. Soil temperatures two inches deep in the planting hole that are at or above 70o F reduce SCM egg laying and larval survival. If soil temperatures are above 70o F at planting but fall below this level for several days in a row, SCM adults will begin to oviposit eggs at the base of transplants. When wilted transplants are inspected in the field, maggots are often not found (they have already pupated), but their tell-tale damage can be seen as a hollowed out stem or root held together by a few strands of plant material. The use of treated seed gives only marginal control of SCM. Replacing dead transplants is the only solution after SCMs kill a plant.

Vegetable Crop Insects

Friday, April 11th, 2008

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

Seed Corn Maggots (SCM) Control in Spring Planted Vegetables
We continue to observe flies actively laying eggs in a number of situations including recently plowed fields, especially when a cover crop is plowed under or when manure was applied to a field. Spring planted vegetables susceptible to maggot damage include cole crops, melons, peas, snap beans, spinach, and sweet corn. Control options can include commercial applied seed treatments, or soil insecticides; however, not all options are available for all crops. The hopper box treatment, Latitude (imidacloprid) is available in our area and is only labeled on sweet corn. Please refer to the labels as well as the following link for control options – http://ag.udel.edu/extension/vegprogram/publications.htm.

Peas
Be sure to sample peas for pea aphids as soon as small seedlings emerge. Before the recent rains, weather conditions (cool and dry) were favorable for aphids. On small plants, you should sample for aphids by counting the number of aphids on 10 plants in 10 locations throughout a field. On larger plants, take 10 sweeps in 10 locations. As a general guideline, a treatment is recommended if you find 5-10 aphids per plant or 50 or more aphids per sweep. Be sure to check labels for application restrictions during bloom.