Progress report for GW20-206
In recent years, cereal production in the Pacific Northwest and Intermountain regions of the USA has been threatened by the re-emergence of a devastating pest, known as wireworm. Neonicotinoid seed treatments, the only group of insecticides registered in cereals against wireworms, have failed to deliver acceptable levels of protection. There is currently an urgent need to develop alternative control methods to be used as components of an integrated pest management protocol against this pest. Cruciferous plants are known for their biocidial effects on a wide range of pest conditions (e.g. weeds, insects, pathogens) due to their glucosinolate contents. Here, in a series of greenhouse assays and field trials, we will examine the effects of different mustard species as rotation/cover crops (soil incorporated), as well as their defatted seed meals in reducing wireworm populations, thus damage. For the first time, we will also test the efficacy of a newly developed concentrated seed meal extract, of either mustard species, against wireworms. Further, we will examine any potential impact of our treatments on the beneficial entomopathogenic nematodes, which are locally present as natural enemies of wireworms. Upon successful results, we expect an increase in planting mustard, or application of its products, by growers as a component of an integrated pest management approach, along with current seed treatments. This work will be delivered by a PhD student, in close collaborations with wheat and barley growers and extension educators. Research finding will be disseminated through a wide range of research and extension outlets.
The overall goal of this project is to explore an alternative integrated management tactic to control wireworms in cereal crops. We will achieve this goal through two complementary objectives. Our third objective is designed for effective delivery of findings to our regional stakeholders.
Objective 1: Evaluate the effect of mustard species including yellow (Sinapis alba) and brown (Brassica. juncea) mustard against wireworm, our sub-objectives are set as below:
1a. Investigate the effectiveness of cover crop (soil incorporated as green manure), defatted seed meals and concentrated extracts of yellow (S. alba) and brown (B. Juncea) mustard species to reduce wireworm damage in wheat under greenhouse conditions.
1b. Evaluate and compare the effectiveness of brown (B.juncea) and yellow (S.alba) mustard rotations, and mustard species products) in reducing wireworm damage to wheat.
Objective 2: Compare entomopathogenic nematode presence and infectivity following yellow and brown mustard treatments, and in relation to non-treated controls.
Objective 3: Disseminate findings to stakeholders and growers and promote adoption of successful IPM tactics against wireworm.
This project not only examines the effectiveness of alternative approaches to reduce wireworm pressure but also aims to increase grower’s knowledge of an alternative to paraphyletic application of synthetic insecticides to promote sustainability of our management practices.
Studies on the efficacy of mustard and mustard products have yielded conflicting results. The species of mustard and targeted wireworm, environmental conditions and timing of application have been proposed as potential variables that can explain the inconsistency in outcomes. In this proposal, focusing on a single wireworm species, sugar beet wireworm, we will evaluate the efficacy of both yellow and brown mustard species, their seed meals, as well as the newly developed concentrated extracts for each of the two species (containing higher concentrations of glucosinolates), while taking into consideration, any potential side-effects on beneficial entomopathogenic nematodes.
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Objective 1: To evaluate the effects of different mustard species and their products against wireworms, we conducted a series of greenhouse and field trials.
Subobjective 1a. Greenhouse studies were developed to minimize the effect of environmental variables and to determine wireworm response to mustard products in the absence of environmental variability. Experiments were conducted at the University of Idaho’s Manis Greenhouse in Moscow, ID. Square plastic pots in the size of 10.16 * 10.16 * 12.7 cm (W* L* H) were selected as experimental pots. Experimental pots were filled with sand-dominated media (70% sand and 25% peat moss). The mixed soil also contained 228 g of vermiculate (Therm-O-Rock West., Chandler, AZ) and 112g of fertilizer (15-9-12 [N-P-K]; Osmocote, Scott-Sierra Horticultural Products, Marysville, OH) per 22 kg of the load. The sugar beet wireworm, Limonius californicus, was used in this experiment. There were 13 treatments: 1) yellow mustard soil-incorporated plant tissue; 2) brown mustard soil-incorporated plant tissue; 3) canola soil-incorporated plant tissue as control; 4) yellow mustard seed meal applied at the rate of 8.9 t/ha (8 g/pot); 5) brown mustard seed meal applied at the rate of 8.9 t/ha (8 g/pot); 6) brown mustard concentrated seed meal extract applied at the rate of 2.2 t/ha (2 g/pot); 7) brown mustard concentrated seed meal extract applied at the rate of 3.3 t/ha (3 g/pot); 8) brown mustard concentrated seed meal extract applied at the rate of 4.5 t/ha (4 g/pot); 9) yellow mustard concentrated seed meal extract applied at the rate of 2.2 t/ha (2 g/pot); 10) yellow mustard concentrated seed meal extract applied at the rate of 3.3 t/ha (3 g/pot); 11) yellow mustard concentrated seed meal extract applied at the rate of 4.5 t/ha (4 g/pot); 12) neonicotinoid seed treatment (CruiserMaxx) and 13) non-treated control. This study was conducted in two time-blocks, with 8 replicates per treatment in each time-block. Yellow mustard (Sinapis alba), brown mustard (Brassica juncea), and canola (Brassica napus) were planted in pots 8 weeks before starting the experiment. At flowering, plants were chopped and mixed onto the potted soil. At the same time, seed meal and concentrated extract of both brown and yellow mustard were added and mixed into the soil for respected treatments. All pots were sealed with parafilm for 24 hours. 300 ml water was added to each pot; in the presence of water, glucosinolate compounds in brown (sinigrin) and yellow (sinalbin) mustard hydrolyze and release the biologically toxic compounds (Popova et al. 2017). Seed meals of both brown and yellow mustard were applied at the rate of 8.9 t/ha (8 g per pot)(Dandurand et al. 2017). Concentrated seed meal extract is a newly developed product and there was no recommended application rate against wireworms. We applied this product at the rates of 2.2, 3.3, and 4.5 t/ha (2, 3, and 4 g per pot, respectively), similar to those applied in (Dandurand et al. 2017) against potato cyst nematodes. A single sugar beet wireworm was placed in each pot immediately after applying the treatments and prior to covering the pots. To minimize phytotoxicity, wheat was planted 14 days after the soil treatments. With the exception of CruiserMaxx treatment, four untreated winter wheat seeds of the cultivar, SY-Ovation, were planted in each pot. CruiserMaxx was applied at the rate of 325 ml/100 kg seeds (CruiserMaxx treatment, only). Pots were arranged in a completely randomized design. After four weeks, emergence rate (percent germination), damage rate (percent damage), and wireworm mortality were recorded. Live wireworms were placed individually in the sand-filled containers and monitored for two weeks for additional mortality.
Statistical analysis was performed in IBM-SPSS (ver. 26). Generalized Linear Mixed Model (GLMM) was used to compare the effects of applied treatments (fixed effect) and time-block (random effect) on wireworm mortality (binomial response).
Subobjective 1b. An on-farm trial was conducted in two wireworm-infested dryland fields and one irrigated field in south-central (1) and southeastern (2) Idaho in Spring 2021. All three fields have been monitored for the presence of wireworms for the last two years. Sugar beet wireworm, Limonius californicus was the most abundant wireworm species in all of our experimental fields.
Study sites: 1) Gordon Gallup field, Ririe, Bonnevile Co., Southeastern Idaho, 2) Hans and Twain Hayden field, Arbon Valley, Power Co., southeastern Idaho, 3) Kimberly R&E Center, Kimberly, Twin falls Co., south central Idaho. The Kimberly field site was added due to its heavy infestation, and the uncertainty about precipitation in dryland (see below).
A total of nine treatments with four plot-replicate per treatment were planned in each location. Treatments included: 1) spring fallow followed by CruiserMaxx-treated winter wheat; 2) spring fallow followed by non-treated winter wheat; 3) spring brown mustard (Brassica juncea) followed by non-treated winter wheat; 4) spring yellow mustard (Sinapis alba) followed by non-treated winter wheat; 5) spring canola (Brassica napus) followed by non-treated winter wheat; 6) spring fallow followed by brown mustard seed meal at the rate of 8.9 t/ha; 7) spring fallow followed by yellow mustard seed meal at the rate of 8.9 t/ha; 8) spring fallow followed by brown mustard concentrated seed meal extract at the rate of 4.5 t/ha; 9) spring fallow followed by yellow mustard concentrated seed meal extract at the rate of 4.5 t/ha. Plots were 10 * 20 ft in size, arranged in a randomized complete block design, with four replicates per treatment. Two weeks before planting all plots were sprayed with Roundup (Glyphosate, Bayer CropScience, CA) to remove weeds. Wireworm numbers were estimated in each plot before planting by using solar bait traps according to Rashed et al. (2015). Spring canola, brown and yellow mustard were planted in the first week of June at the rate of 12 seed/ft in 1-1.5-inch depth (due to the lack of moisture). We proposed to chop and incorporate planted mustard plants into the soil right after flowering. Late planting has been selected to manage the application time of incorporated mustard plants and mustard products in order to maximize their biocidal effects as well as minimize phytotoxicity effects on winter wheat.
Due to very low precipitation and the unusually high temperatures across the state, mustard seed germination was not uniform across locations and resulted in poor stands in two out of our three locations (see below). Therefore, our field trials are to be repeated in the fall of 2021. As such, we adjusted our proposed planting dates to fall mustard planting followed by spring wheat. We will plant brown and yellow mustard in late-August and incorporate them into the soil in October 2021. Similarly, we will apply seed meal and concentrated extract products in late October which will be followed by planting spring wheat in April 2022.
Mustard germination reached 80% in only one of the locations and we chose to proceed with winter wheat planting in late September, following an early August mustard and mustard product incorporations.
Objective 2: To address objective 2, evaluating the impacts of the application of mustard products on beneficial entomopathogenic nematode in the experimental plots, we will take two soil samples from each plot using a 6-inch augur, right before incorporating mustard and applying mustard products. Soil samples will be mixed, and a subsample of 250 g soil will be transferred to plastic containers and five waxworms will be placed in each container. After 2-3 days, dead larvae will be transferred to White traps (White 1927 ) individually and the number of infective juveniles collected from one single waxworm in 1000 µl suspension will be counted and the average of nematodes recovered will be used to estimate the nematode population in each experimental plot in relation to the nontreated controls. This process will be repeated in April 2022 to determine the impact of bioinsecticides on the soil-borne entomopathogenic nematodes.
Greenhouse trial (subobjective 1a)
Wireworm mortality: Wireworm survivorship was significantly affected by treatment (F= 2.23, df = 12, 192, p = 0.012). Brown mustard (B. juncea) concentrated seed meal extract, applied at the rate of 4.5 t/ha (4 g/pot), resulted in the highest wireworm mortality, which was significantly higher than the nontreated control and brown and yellow mustard seed meals. Wireworm mortality did not appear to be influenced by the rate of application of the brown mustard concentrated extract. Although yellow mustard concentrated extract, applied at the rate of 4.5 t/ha, resulted in significantly higher mortality than its lower rates (i.e., 37.5 % and 20%) and the nontreated control treatment, its efficacy was relatively lower than those of brown mustard concentrated extracts (Fig. 1).
Emergence success: Plant emergence in the greenhouse was significantly affected by treatment (F= 7.533, df = 8,811, p < 0.001). The rate of emergence was the highest for the CruiserMaxx treatments. No significant difference was detected in plant emergence among other treatments. It is important to note that the rate of emergence was considerably low across all treatments (12.93% -32.64%), except for the CruiserMaxx treatment (78.52%). This experiment will be repeated with a different seed batch to assure that the low emergence rate has not been due to poor seed quality.
Overall, our greenhouse findings have suggested that the application of brown mustard concentrated extract product can be effective in reducing wireworm numbers. However, mortality caused by the brown mustard green manure (applied as plant tissue or concentrated seed meal) did not differ from that of the nontreated control. Due to their high glucosinolate content, several plant species from the Brassicaceae family can be used as biocides against a wide range of pests including insects, weeds, and pathogens. (Lichtenstein et al. 1964, Mojtahedi et al. 1993, Williams et al. 1993, Hansson et al. 2013, Dandurand et al. 2017). However, different species of mustard like brown and yellow mustard have different glucosinolate compounds. The major compound in the yellow mustard, S. alba, is sinalbin, which in the presence of water is hydrolyzed and produces a phytotoxic compound known as isothiocyanate (Popova et al. 2017). Isothiocyanate (-SCN) has mostly been suggested to have herbicidal effects and is less effective against insect pests like wireworm (Papavizas 1966, McCaffrey et al. 1995, Mojtahedi et al. 19914). Yellow mustard plant tissues and seed meal applied as green manure were not effective in reducing wireworm numbers. Yellow mustard concentrated extract causes relatively higher mortality on sugar beet wireworm only when applied at the higher rate of 4.5 t/ha. Our findings supported those by McCaffery et al. (1995) who suggested SCN-, the toxic compound in yellow mustard was not effective in reducing wireworm population (McCaffrey et al. 1995).
There are some studies suggesting brown mustard efficacy against pests including wireworms (Furlan et al. 2004) and Globodera spp. (Dandurand et al. 2017). In our greenhouse experiment, soil incorporated brown mustard caused 31% mortality in sugar beet wireworm, which was relatively, but not significantly, higher than the mortality observed in the control treatment (6.25%). However, 65% wireworm mortality was achieved through applying brown mustard concentrated extracts. To find the effective rate of concentrated extract against wireworm, we evaluated the three rates of 2.2, 3.3 and 4.5 t/ha, similar to those applied in Dandurand et al. (2017) against the potato cyst nematode; we observed no significant difference in wireworm mortality among application rates. Although yellow mustard is known for its phytotoxicity, seed emergence success was not significantly different across treatments, except for CruiserMaxx. The greenhouse study will be repeated to determine the underlying cause for the observed poor wheat emergence. Our field trials are also expected to validate our greenhouse findings. However, as mentioned earlier due to the unusual drought and heat stress our field planting are set to be repeated in fall. We expect field results to be available by the next reporting period
Education and Outreach
The findings and plans for this research project were shared through webinars (Soil Health, WSU; Alternative Crop Advisory meeting, see below) and the online cereal school for Idaho producers (grower training/presentation), where more than 200 cereal producers and agricultural professionals participated. One peer-reviewed abstract (see page 19) has been published in the 2021 Dryland Field Day with the contribution of three universities in PNW, including the University of Idaho, Oregon State University, and Washington State University. PhD student Nikoukar presented the effects of mustard species and their product as an alternative control approach against wireworm in the 2021 Alternative Crop Advisory Board meeting for cereal producers, extension educators, and researchers (no link available). This project was introduced and discussed in two field days held in Idaho Falls and Aberdeen, Idaho in July 2021.