SCEPTREplus: Leafy salads

EAMUs secured

Authorisations secured following SCEPTREplus trials for leafy salads:

• Devrinol as a herbicide for herbs and spinach
• Venzar 500SC as a herbicide for outdoor leafy vegetables and fresh herbs
• Emerger as a herbicide for root crops, alliums and celery

Celery herbicide screen

• Crop: Outdoor Celery
• Target: Broadleaf weeds
• Period: April 2017 to March 2018 and April - Dec 2019

The bulk of the UK celery crop is grown on peaty soils. Because of the high organic matter of these soils, the overall activity of residual herbicides is generally reduced and their length of persistence in the soil is shorter.

This trial therefore concentrated on potential new post-emergence contact herbicides which may be used to partly or fully replace the current use of linuron.

Conclusions

Year one:

All of the tested products reduced weed ground cover when compared to the untreated control. The best weed control with the least corresponding crop damage was given by the standard commercial practice treatment of pendimethalin plus linuron followed by a second linuron. Of the new products tested the best weed control was achieved by two applications of AHDB9994. Also giving good weed control was a treatment of pendimethalin plus prosulfocarb plus AHDB 9995 followed by AHDB 9974.

AHDB9994 caused some leaf bleaching on the treated leaf, similar to symptoms seen from clomazone, although the untreated leaves appeared to grow away normally as they do with clomazone. AHDB 9974 also caused some leaf damage, this time leaf scorch on the edge of the older leaves, again new leaves developed normally from the center of the plant.

The site was very weedy with the untreated plots reaching 100% weed cover by 3 weeks after planting. None of the treatments prevented plots from being overcome by weeds with even the best treatments at 70% weed cover at 6 weeks after treatment.

Year two: 

None of the treatments on their own would give sufficient weed control to be commercially acceptable, however a combination of Stomp Aqua (pendimethalin) plus Defy (prosulfocarb) followed by AHDB9864 would likely be the best treatment and improve weed control for celery. Emerger or AHDB9997 used sequentially following treatment by the commercial standard would also give a significant improvement to the current commercial practice.

Approvals should be sought for Emerger at a 60 day PHI and AHDB9864, AHDB9997 with a 60 day or shorter harvest interval.

• Crops: Lettuce and baby leaf spinach
• Target: Broadleaf weeds and grasses
• Period: April 2018 - Jan 2019 and April 2019 to Dec 2019

The first year trial aimed to look at new post-planting options for broadleaf weed control for transplanted lettuce, recording efficacy and crop safety. An additional aim was to evaluate the crop safety of AHDB 9985 when applied to lettuce.

In the second year we looked at new pre-and post-emergence options for broadleaf weed control for drilled baby leaf spinach, assessing both the level of weed control and crop damage.

Conclusions

Year one:

AHDB 9877 would give growers a useful extra option for post-planting weed control. To ensure crop safety, use would be recommended at 1.0 L/ha or below. AHDB 9985 would be a useful addition to aid grass weed control in lettuce if an authorisation was gained. Label rates were shown to be safe in the trial. Further work would be required with AHDB 9876 as it is new, and gives dramatic crop effects, but the crop does subsequently recover.

Year two:

No pre-emergence products gave the same combination of crop safety and weed control as Venzar Flo applied pre-emergence. However, there are promising options which could improve weed control at a post-emergence timing. These are AHDB 9853 and AHDB 9864 although these are on the margins of crop safety. Further work is required on rates and timings and to understand how to integrate them safely into programmes.

Treatments to reduce Fusarium wilt of lettuce

• Crops: Lettuce
• Target: Fusarium oxysporum f. sp. Lactucae race 4 (FOL 4)
• Period: Jun 2018 - Feb 2019

Fusarium wilt of lettuce, caused by Fusarium oxysporum f. sp. Lactucae race 4 (FOL 4) was first reported in the UK in October 2017. A pot-based glasshouse experiment and a polytunnel trial were carried out to identify chemical and biological treatments to reduce disease caused by FOL4

Conclusions

Single applications of the chemical fungicides tested in the glasshouse trial were not adequate for control of FOL4.

Three applications of some biological control agents were effective.

The soil fumigant Basamid was very effective in preventing FOL4 in both the glasshouse and polytunnel trials. There was some evidence of phytotoxicity in the polytunnel trial, most likely due to inadequate time between application and planting. Note that Basamid is limited to one application every three years.

The biological control treatment T34 reduced FOL4 development in the pot-based glasshouse trial, but not in the polytunnel trial. However, the latter was conducted in cold conditions which most likely compromised control efficacy.

Prestop showed some efficacy for control of FOL4 in the glasshouse trial (not tested in polytunnel).

None of the chemical fungicide treatments reduced FOL4 with the exception of Previcur Energy in the glasshouse trial. However, this treatment was not as effective as T34 or Prestop and only delayed the development of symptoms.

• Crops: Lettuce
• Target: Phytophthora cryptogea and other oomycete root rot pathogens
• Period: Feb - May 2018

UK hydroponic lettuce growers currently have no access to fungicides (conventional or biopesticide) that are approved for application into hydroponic growing solution for direct control of root rot disease. A selection of conventional and biopesticide products were tested, in a novel hydroponic test system, for efficacy against root rot in lettuce caused by P. cryptogea.

Conclusions

Two conventional fungicides (AHDB 9942 and AHDB 9940) gave excellent control of disease symptoms and one other (AHDB 9939) gave some control. No biopesticides were effective at reducing the symptoms of root rot, although one that caused phytotoxicity did seem to reduce the number of zoospores present in the nutrient solution and might be useful at a lower, nonphytotoxic, application rate.

Root rot disease in deep water hydroponic systems, caused by P. cryptogea, can be managed using fungicides applied directly into nutrient solution, although approvals for this method of application will need to be sought.

• Crops: Protected lettuce (model crop approach applicable to other protected edible, field vegetable, soft fruit and ornamental crops
• Target: Downy Mildew, Bremia lactucae
• Period: Aug - Oct 2017

This trial took a model crop approach, so the results would also be applicable to downy mildews in many other crops, including: Lettuce (outdoor), cucumber, herbs, brassicas (propagation and field crops), onions (bulb and salad), red beet, ornamentals (including hardy nursery stock, pot and bedding plants), peas and beans, hops, soft and cane fruit, and vines.

Novel conventional fungicides and biopesticides were screened for effectiveness. Once promising products have been identified more cropspecific studies can be undertaken, in particular, crop safety studies.

Conclusions

The level of disease was low-moderate throughout the trial. The standard programme performed as would be expected - it reduced downy mildew infection levels to a certain extent, but did not completely control the disease.

One biological product (AHDB 9957) gave statistically significant levels of control compared to the untreated at the first two assessments. At the end of the trial, all conventional products gave significant levels of downy mildew control compared to the untreated plots.

The two conventional products which were applied late appear to have had some eradicant activity, with levels of downy mildew being reduced to significant levels 9 days after application of AHDB 9959 and 16 days after application of AHDB 9958.

One product (AHDB 9963) left a visible residue on the foliage, even after just one application, and one product (AHDB 9958) was phytotoxic, causing small necrotic spotting on the leaves. 

• Crop: Celery
• Target: Septoria leaf spot
• Period: May - Oct 2018

The two year study investigated new seed treatments and foliar applied products for control of Septoria leaf spot for use in both organic and conventionally produced celery.

A further trial explored possible seed treatments.

Conclusions

Foliar applications

All nine conventional fungicide treatments provided significant levels of Septoria leaf spot control by the end of the trial. The two biopesticides examined did not provide a significant level of control during the trial, a possible consequence of these products not being rain fast and so may have been washed off the plants. An EAMU for Nativo 75WG to control leaf spot in celery has recently been gained with an EAMU for another in the pipeline.

Seed treatments

In a comparison of treatments, the industry standard (warm water and thiram soak) remains the most effective treatment in reducing celery Septoria without affecting seed germination or vigour. However, encouraging results were obtained with hydrogen peroxide and to a lesser extent AHDB 9850, despite small reductions in germination rates. Further work is required to identify effective dose rates for application to commercial practice and as a replacement for current chemical control products.

• Crops: Lettuce
• Target: Lettuce root aphid
• Period: May - Oct 2018 and May - Aug 2019

There are currently a limited number of control options for lettuce root aphid. Approval for the standard treatment, Cruiser, has been revoked.

Initial to evaluate new and alternative insecticide options were unsuccessful due to low infestation levels, so were repeated the following year.

Conclusions

There was no indication of lettuce root aphid control from any of the test treatments. Alternative approaches to managing lettuce root aphid infestations need to be explored.

• Crops: A range of crops (Strawberry, cherry, raspberry, blackberry, apple, pear, blackcurrant, cucumber, celery, potato, tomato)
• Target: Capsid bugs
• Period: Sept 2018 – Jan 2019

Management of these pests currently relies on application of broad-spectrum insecticides. These can be effective at killing capsids, but also reduces numbers of the naturally-occurring and released natural enemies to control other pests.

This review aims to identify capsid control options that may form basis of further research including efficacy trials.

Conclusions

• Insecticides with more selective activity against sap-feeding pests, and lower impact on beneficial natural enemies (e.g. sulfoxaflor and flonicamid) have become preferred interventions for capsids in Australia and the USA
• Novel insecticides with alternative modes of action are available for testing against capsid pests
• Improved formulation of insecticides may be possible. This may be achieved by mixing with salt or enclosing them in attractant-coated microcapsules
• The entomopathogenic fungi Beauveria bassiana and Metarhizium brunneum are available as commercial formulations and should also be considered as candidates for inclusion in efficacy testing.
• Particular weeds (e.g. nettles) are assumed to be linked with capsids and control of these is recommended
• More information is needed on the role played by natural enemies
• Semiochemical-based approaches (including push-pull strategies and pheromone based monitoring traps) have been developed for capsids as part of previous AHDB-funded work and have potential for further refinement

Aphid control

• Crops: Carrots, lettuce, brassicas
• Target: Myzus persicae, Brevicoryne brassicae, Cavariella aegopodii, Nasonovia ribisnigri
• Period: Dec 2017 – March 2019

Conclusions

Evaluation of a range of insecticide and bio-insecticide treatments for their efficacy against four species of aphid infesting vegetable and salad crops.

The main study showed that a number of ‘novel’ insecticides and a few bio-insecticides were effective against one or more species of aphid. Some of the insecticides showed good persistence. The study also highlighted the importance of product formulation and adjuvants in increasing levels of control.

The additional study showed that a number of products were effective as foliar sprays and that some of them may also control foliage aphids when applied as phytodrip treatments, although it would obviously be advisable to test such treatments in the field and to evaluate the persistence of such treatments.