Posts Tagged: broccoli
Cabbage maggot (Delia radicum) is a serious insect pest of Brassica crops such as broccoli and cauliflower in the Central Coast of California. These crops are grown throughout the year; as a result cabbage maggot problems persist year long.Cabbage maggot eggs are primarily laid in the soil around the crown area of the plant. A single female fly can lay 300 eggs under laboratory conditions. The eggs hatch within 2-3 days and the maggots feed on the taproot for up to three weeks and can destroy the root system of the plant. The maggots pupate in the soil surrounding the root system and emerge into flies within 2-4 weeks. Severe cabbage maggot feeding injury to the roots cause yellowing, stunting even plant death.
Control of cabbage maggot on Brassica crops primarily involves the use of soil applied organophosphate insecticides such as chlorpyrifos and diazinon. However, the persistent use of organophosphate insecticides has resulted in high concentrations of the insecticide residues in the water bodies posing risks to non-target organisms and public health through contaminated water. Currently, use of organophosphate insecticides is strictly regulated by California Department of Pesticide Regulation. There is therefore an urgent need to determine the efficacy of alternate insecticides for cabbage maggot control.
The efficacy of 29 insecticides was determined against cabbage maggot through a laboratory bioassay by exposing field collected maggots to insecticide treated soil immediately after application. Three parameters were used to evaluate efficacy (1) proportion of maggots on the soil surface after 24 h, (2) proportion of change in weight of turnip bait, and (3) dead maggots after 72 h. Based on the assays, 11 insecticides performed better and they were Mustang, Torac, Danitol, Belay, Capture, Warrior II, Lorsban, Mocap, Durivo, Pyganic and Vydate in the order of highest to lowest efficacy. Eight insecticides were selected based on superior efficacy to determine the length of residual activity on cabbage maggot larvae. The persistence of insecticide activity was greater with Capture, Torac and Belay than with other insecticides tested.
The mode of exposure of insecticides in this study was entirely by contact (through skin) and other modes of exposure such as ingestion (through mouth) or through respiratory holes (spiracles) were not investigated. Some of the insecticides tested in the study were insect growth regulators (IGRs) (Dimilin, Rimon, Trigard, and Aza-direct), which normally interfere with the growth and development of the insect and they showed a low efficacy against cabbage maggot larvae. Entrust (spinosad) showed a moderate efficacy possibly because the primary mode of exposure to Entrust is by ingestion. The diamide insecticides (Beleaf, Coragen and Verimark) have systemic activity as they move within the plant and likely away from the site of application. It is possible that the soil applied diamide insecticides are absorbed by the roots and translocated to the above ground plant parts with little effect on the feeding larvae in the tap roots.
This study was conducted under controlled conditions in the laboratory and the results may not be entirely consistent in field conditions. The Brassica fields in the California's Central Coast are profusely sprinkler irrigated up to three weeks after sowing to ensure uniform germination and proper establishment of plants. It is likely that applied insecticides are partially or completely leached out of the root zone area without providing anticipated maggot control. In this study, insecticides were drenched into the cup and none of the applied insecticide solution leached out. Therefore, it is likely that the insecticides were more effective in the laboratory assay than they would be in the field. Certain insecticides such as pyrethroids tend to bind to the soil organic matter. The organic matter in the California's Central Coast soils can be up to 4%, which could reduce the availability of soil applied pyrethroid insecticide to the root zone where cabbage maggot larvae typically colonize. In situations with poor insecticide spray coverage, invading cabbage maggot larvae are possibly exposed to no or sub-lethal doses of the soil applied insecticide and may be able to penetrate the soil and infest the roots. The air temperature in the field at the time of insecticide application may influence the efficacy of the applied insecticide. The efficacy of pyganic decreased as the temperature increased against onion maggot. This suggests that application of pyrethroid insecticides should be avoided during warmer periods of day.
Other field conditions that influence efficacy of insecticides are cabbage maggot incidence and frequency of invading cabbage maggot flies on Brassica crop in the Central Coast of California. The earliest peak of cabbage maggot infestation occur a month after sowing broccoli seeds and infestations can be continuous until harvest. Also, insecticides applied at sowing as a banded spray on the seed lines did not provide adequate cabbage maggot control based on the insecticide efficacy trials conducted in commercial broccoli fields. These findings suggest that delaying the insecticide application by 2-3 weeks after sowing is more likely to maximize maggot control. Because the cabbage maggot infestation can last several weeks, insecticides with extended persistence of efficacy would increase the value for cabbage maggot control. Overall, results show that Capture, Torac and Belay which performed effectively against cabbage maggot for a month after application. This indicates that insecticides used before the first peak of infestation may protect the younger stages of the Brassica plants allowing them to establish and tolerate milder cabbage maggot infestations thereafter.
In conclusion, 11 insecticides with high efficacy were identified for future investigation. Future studies will focus on determining the effects of application timing and delivery methods compatible with cabbage maggot incidence in both directly sown and transplanted Brassica crops in the Central Coast of California.
If you are interested in reading the details of this study, please click the link below to access the published article.
Cabbage maggot infested broccoli root
Cabbage maggot infested cauliflower field
Cabbage maggot infested cauliflower field
Comparison cabbage maggot infested and uninfested roots
Insecticides tested against cabbage maggot
Insecticides tested against cabbage maggot (continues...)
Efficacy of insecticides based on larvae failed to penetrate the soil surface. The abbreviation L = lower rate and H = higher rate
Efficacy of insecticides based on number of larval death. The abbreviation L = lower rate and H = higher rate
Efficacy of insecticides based on amount of unfed turnip bait. The abbreviation L = lower rate and H = higher rate
The garden symphylan (Scutigerella immaculata) (Figure 1), a white, highly mobile, centipede-like, 1/4 inch long soil arthropod, is a serious soil pest of several high-value crops in the Central Coast of California such as lettuce, strawberry, broccoli, cauliflower, artichoke and celery. The garden symphylan feeds on roots of both direct-seeded and transplanted crops alike causing severe stunting and plant mortality. Besides feeding on the roots, they also survive feeding on organic matter, and other soil dwelling fungi. The garden symphylans use the channels created by other soil organisms such as earthworms for vertical and lateral movement through the soil profile. Their seasonal movement in the soil is also influenced by soil moisture, and temperature. Incidence of garden symphylan infestation is mostly reported in heavier or clay soils with higher organic matter content than lighter or sandy soils. The garden symphylans spend their entire life in the soil and are well adapted to the subterranean habits. They lack eyes but have long antennae and thousands of sensory hairs on the body, which possibly help taste and feel the surroundings.
The garden symphylans are primarily managed using preventative insecticide application, although other tactics such as crop rotation, planting less susceptible crops, flooding the field, reduced tillage, and conservation of beneficial organisms have been suggested. Success and effectiveness of these non-chemical tactics were constrained by several factors such as lack of fit to the current production practices, susceptible crops being grown, varied topography, and enormous population size.
It is important to remember that garden symphylans are very difficult to manage because of their behaviors such as high mobility, and their adaptations to the soil conditions. They can move to deeper soil layers when conditions are not favorable in the upper soil layers (such as high temperature or low water content). Often, garden symphylans aggregate in high densities in certain spots in the field and the damage is concentrated in those spots (Figure 2). Thus, it is very difficult to predict their incidence and plant damage in the field.
One strategy to manage garden symphylans is to determine which insecticides would repel garden symphylans in the soil. This will at least provide some control until the seedling establish in the soil. Studies were conducted to establish relative efficacy of insecticides against garden symphylan based on repellency behavior and how many died. Based on the studies, Belay, Vydate, Mustang, Lorsban, Mocap, Aza-direct Leverage and Torac showed signs of repellency to garden symphylans. Aza-direct is the only organically approved insecticide that elicited repellency. The insecticides, Capture, Vydate, Belay, and Mustang caused 44 to 95% garden symphylan dead. 100% of the garden symphylans were killed when Torac was used. Torac is not registered on any crops at this moment. These studies provide guidelines on efficacy of insecticides against garden symphylans. For further reading please click the link below to access the published article.
Cabbage maggot (Delia radicum) is one of the most destructive pests of cruciferous crops in the Salinas Valley. Cabbage maggot flies lay eggs in the soil around the base of the plant. A single female can lay about 300 eggs under laboratory conditions. Legless,8-mm long white-maggots feed on the taproot and affect normal plant development. After about 3 weeks of feeding, the maggot pupates in the surrounding soil and remains at this stage for 2-4 weeks before emerging into an adult fly. The most common above-ground feeding symptoms of cabbage maggot are yellowing, stunting and slow growth.
Because the winter weather in the Salinas Valley is mild and rarely goes below freezing point, not all cabbage maggot pupae go into a resting stage, often called as diapause. This means our unique environment enables cabbage maggot flies to remain active even in winter months, producing multiple overlapping generations throughout the year. In this post organophosphate era with stringent restrictions for chlorpyrifos and diazinon use and less persistent insecticides being available for cabbage maggot management, knowledge of field-level incidence of cabbage maggot infestation is critical to determine precise timing for insecticide applications in brassicas. We studied the temporal incidence of cabbage maggot relative to seeded broccoli and turnip in the Salinas Valley.
Cage studies showed that severe injury from cabbage maggot did not appear during the first 14 days after plant emergence but was greater during 15-28 days after plant emergence. Similarly, survey in broccoli fields indicates that cabbage maggot flies did not lay a high number of eggs at the base of the plant until three weeks after plant emergence, despite presence of adult cabbage maggot in the field during the early stages of plant development (Figures below). On turnip, notable injury from cabbage maggot did not appear until five weeks after plant emergence. This is important information because typically insecticides targeting cabbage maggot were applied mostly at planting. Researchers showed that cabbage maggot infestation could be suppressed by using organophosphate insecticides, particularly chlorpyrifos, for more than a month after planting because product residues persisted for an extended period. However, most of us are not using these insecticides and a consistent cabbage maggot control using organophosphate insecticides was never attained in the Salinas Valley. I'm working on insecticides to determine their effectiveness against cabbage maggot and will share that information as soon as it is available.
It is unclear why increased cabbage maggot oviposition did not occur during the early stages of plant development. It is possible that the invading cabbage maggot flies cannot distinguish the young seedlings at a certain size relative to the surrounding area of bare soil. Cabbage maggot populations and crop injury from this pest tend to be more abundant in the border than the interior zone of the field; this invasion pattern continues throughout the growing period. In conclusion, our data suggest that the important season periods in the central coast vegetable production area to consider targeting cabbage maggot control are three to four weeks after planting the seeds. I will continue to monitor if other maggot species (seedcorn maggot or onion maggot) which could attack when brassica plants are at younger stages especially during spring or early summer.
For those of you, who are interested to read more on it, please find the published article after clicking the link (below) and feel free to contact me (Shimat Joseph) at email@example.com or 831 759 7359.
Bulb mites (Rhizoglyphus spp. or Tyrophagus spp.) (Photo 1) are known to attack spinach, onion and garlic but recently I have observed them feeding on germinating seeds of broccoli (Photo 2). Cool and wet soil conditions especially during early spring, trigger rapid multiplication of these mites in the soil and they infest germinating seeds. These mites often feed on the internal content of the seeds leaving behind only the seed coat. Severe infestation will result in inconsistent crop stand (Photo 3, and 4). Those affected seedlings would have distorted shoot and/or delayed germination (Photo 5). Cotyledon leaves of those affected seedlings would have damaged margins (Photo 6). Unlike the damage from garden symphylan which appears in hot spots in a field, bulb mites affect the entire crop stand (Photo 3).
Bulb mites seem to be composed of several species of soil mites including crown mites. Bulb mites are shiny, spherical and clear or off-white in color. These mites often have distinctive long hairs on their abdomen. These mites survive on the decaying plant material in the soil.
Bagrada bug, Bagrada hilaris is now well established in the southern region of the Salinas Valley. This invasive stink bug, if left unmanaged, could become a serious pest of brassica crops. We studied their occurrence on cover crop, a mustard cover crop blend, broccoli and surrounding weed species, and would like to report few observations.
1. Cover crop, mustard
We observed significant populations of bagrada bug on 4-5 week-old mustard cover crop blend (Brassica juncea and Sinapis alba) in San Ardo. Interestingly, the adjacent field was also cover cropped with mustard but was disced few weeks ago. It is likely that the previous adjacent mustard crop might have had a bagrada bugs infestation and they moved to new planting when it was disced. When we walked into mustard stand from the disced field, we noticed that number of bagrada bug numbers declined from the field edge to the interior of the field. To understand better, a border zone (edge of the field), interior zone (90 feet into the field), and intermediate zone (between border and interior zones) were designated. Within each zone, six spots (~ 5.6 feet) were randomly selected and number of bagrada bugs was quantified after spending two minutes per spot. Similarly, two weed species and one native shrub surrounding the mustard field were randomly selected and number of bagrada bugs on them was counted after spending about one minute per plant.
Bagrada bugs tend to be more abundant on the edge of field than interior zones of the field (Fig. 1). It seems that bugs settled on the border plants of the field rather aggressively moving into the field. All life stages were detected. Most of the adults were in the mating position (connected by the rear ends) but very mobile. The adults tend to hide into the soil or under the leaves when we approached the infested plants.
Among the weed species investigated, bagrada bugs were only found on short pod mustard (Fig. 2 and 3). Other weed species investigated were shortpod mustard (Hirschfeldia incana), common purslane (Portulaca oleracea), lambsquarter (Chenopodium album), and the native shrub coyote bush (Baccharis pilularis). It is interesting to note that shortpod mustard plants were senescing, yet we found bagrada bugs on them.
The broccoli field was located in San Ardo adjacent to the Salinas River. The riparian plant community along the river contained stands of perennial pepperweed (Lepidium latifolium) as well as other species. Bagrada bug infestation was severe on pepperweed (Figs. 4a, and b).
Bagrada bug feeding injury symptom on broccoli plants was clearly visible on plants along the edge of the field. Feeding injury symptoms on broccoli include leaf distortion, chlorotic patches along the leaf margin and stunting (Fig. 5). Again, feeding symptoms drastically declined and/or plant vigor improved as we walked few steps (~ 10 feet) into the broccoli field from river side. Both nymphs and adults of bagrada bug were active along the edge of the field.
These preliminary observations indicate that some plants in the mustard family are highly attractive to bagrada bug. Shortpod mustard is a common summer-growing species that is commonly found on roadsides, in vineyards and in rangeland. Perennial pepperweed is an invasive plant that is commonly found in the riparian strip along the Salinas River. Both plants provide sufficient food resources for bagrada bug to successfully breed. After the onset of the winter rains, other mustard family weed species such as field mustard (Brassica rapa), black mustard (B. nigra), London rocket (Sisymbrium irio) and wild radish (Raphanus sativus) will begin their growth cycle. These plants are very common along roadsides and in ditches and may also provide over wintering habitat for bagrada bug.