Evaluating the Efficacy of Organic Approved Fungicides for the Control of Powdery Mildew in Squash

Powdery mildew grows well in environments with high humidity and moderate temperatures and can be problematic on crops in the Northeast. Cucurbit crops face powdery mildew and often downy mildew on a yearly basis and significant yields losses have been reported. The family of cucurbits is an important part of the diversified crop mix of a typical commercial vegetable farm in Vermont and throughout the Northeast. Growers have been using cultural practices, fungicides, and multiple plantings to mitigate crop loss from powdery mildew, however, the impact of the disease is seasonally dependent and still represents a consistent loss

Intracellular mycoparasites in action: interactions between powdery mildew fungi and Ampelomyces

Pycnidial fungi of the genus Ampelomyces are widespread intracellular mycoparasites of powdery mildew fungi worldwide. Their pycnidia are produced in hyphae, conidiophores and immature ascomata of their mycohosts. Thus, they suppress both the asexual and the sexual reproduction of the invaded powdery mildew mycelia, and then destroy them completely. Conidia of Ampelomyces are released from the intracellular pycnidia by the rupture of the pycnidial wall; conidia then germinate on the host plant surfaces, penetrate the intact hyphae of powdery mildew mycelia found in their vicinity and invade them internally growing from cell to cell through the septal pores of the mycohost. The early stage of mycoparasitism is apparently biotrophic, but the invaded cytoplasm then begins to die and a necrotrophic interaction results. Toxin production has not been detected in Ampelomyces, so it might act directly by invasion and destruction of the host cytoplasm. Experimental data showed that parasitized powdery mildew colonies can continue their growth, but their sporulation is stopped soon after Ampelomyces penetrated their mycelia. It is concluded that these mycoparasites represent a stress factor in the life cycle of their mycohosts but their role in the natural control of powdery mildew infections requires further investigations

Susceptibility to Apple Scab, Nectria Cancer and Powdery Mildew of Different Unsprayed Apple Varieties

Twentyfive apple varieties were evaluated for Apple scab (Venturia inaqualis), Nectria canker (Nectria galligena) and Powdery mildew (Podosphaera leucotricha) for 4 to 7 years. The trees were grown unsprayed. The weather conditions at the experimental orchard normally results in high infections of apple scab and low infections of powdery mildew. Infections of Apple scab is often seen also in scab resistant varieties. Williams Pride, Katinka and Katrina (scabresistant varieties) were the only varieties not showing scab in the experimental period. The two scabresistant varieties Angold and Produkta (varieties having a poor fruit quality) was unsusceptible to Nectria canker. The reference variety Elstar/Elshof was in all plantings among the most resistant varieties. Powdery mildew is not a problem at the experimental orchard. Most varieties had low susceptibility to Powdery mildew. Varieties with low susceptibility to diseases in general were Angold, Produkta, Rajka, Rubinola, Ahrista, Gerlinde, Gul Richard, Sukkertop, Katinka, Katrina, Marian and Primicia

Hops Crowning Trial

As the acreage of hops continues to rapidly expand in the northeast, there is a great need for production knowledge specific to our region. Downy mildew has been identified as the primary pathogen plaguing our hop yards. This disease causes reduced yield, poor hop quality, and can cause the plant to die. Control measures that reduce disease infection and spread while minimizing the impact on the environment are desperately needed for the region. Mechanical control is one means to reduce downy mildew pressure in hop yards. Scratching is a practice initiated in the early spring when new growth has just emerged from the soil. The first shoots have an irregular growth rate and are not the most desirable for producing hop cones later in the season. Removal of this new growth through mechanical means helps to remove downy mildew inoculum that has overwintered in the crown. The top of the crown itself can be removed to further eliminate overwintering downy mildew. This practice is typically referred to as “Crowning”. While crowning is known to be effective in the Pacific Northwest, there is no established time frame for crowning in the Northeast. The goal of this project was to evaluate the impact of crowning/scratching at two different time periods on hop downy mildew pressure as well as hop yield and quality

Impact of foliar diseases in organically grown barley: Influence of fertilization, nutrient content in leaves, varietal disease resistance characteristics and yield potential

Significant increase in severity of powdery mildew,leaf rust and net blotch with increasing N-content in plant leaves 30 days after germination (all years where the relevant diseases were present at a substantial level). This may explain: · Most of the environmental main effects (field) on disease. · Effect of treatments, i.e., treament 4 resulted in reduced N/increased K content in leaves, which coincided with reduced levels of disease. We observed no clear effect of P, Ca, S, and Zn content in leaves on disease. Micronutrients as Cu, Mo and Mn showed significant effects on powdery mildew in one year but not the other; further interpretation may not be possible due to inter-correlation among the effect of micro-nutrients. The diseases had a significant yield reducing effect, in particular powdery mildew and net blotch, which occurred at highest severities. In addition, net blotch affected root development, resulting in significant shorter roots, whereas powdery mildew did not. The effect of disease on root length was of the same order of magnitude as the factor 'variety', but larger than effects of 'year'

An assessment of apple varieties for their suitability in organic production systems

Twenty seven varieties of apple were assessed for their susceptibility to apple scab, mildew and rosy apple aphid in a replicated experiment at East Malling Research. The varieties most affected by mildew were Goldrush, DL11, Liberty, Bohemia and Pinova. Ceeval, Discovery, Edward VII, Howgate Wonder, Rajka, Rebella and Topaz had the lowest incidences of mildew. The highest incidence of scab occurred on Pilot and Pinova, but infestation was low throughout the assessment period. In 2006 when aphid populations were high, Liberty, Goldrush and Delorina had no aphid infestations, and low infestations were seen on Edward VII, Resi and Santana

Efficacy testing of novel organic fungicides and elicitors: from the lab to the field

Novel organic fungicides and elicitors against downy mildew on grapevines were evaluated on grapevine seedlings in a series of indoor screening experiments under controlled conditions and, if they have shown a good efficacy indoors, in a screening vineyard under field conditions. From 39 products tested under controlled conditions 10 were further examined under field conditions. All of the new products tested under field conditions showed at least partial efficacy. However, the efficacy was not good enough to protect grapevine plants sufficiently from downy mildew. For a complete re-placement of copper in plant protection against downy mildew on grapevine in organic agriculture, additional new products are needed

Hop Biofungicide Trial

Downy mildew has been identified as the primary pathogen plaguing northeastern hop yards. This disease causes reduced yield, poor hop quality, and, in severe cases, plant death. Control measures that reduce disease incidence and have a low environmental impact are desperately needed for the region. Regular application of protectant fungicide sprays is an effective method for managing downy mildew pressure in hop yards. However, regular chemical applications can lead to residual toxicity in the soil and have a negative effect on beneficial organisms. Extended use of protectant and curative fungicides can also lead to pathogen resistance. The goal of this project was to evaluate the efficacy of organic approved biofungicides with a variety of active ingredients for control of downy mildew in hops

Resistance to the SDHI fungicides boscalid and fluopyram in Podosphaera xanthii from commercial cucurbit fields in Spain

Powdery mildew elicited by Podosphaera xanthii is a devastating disease of cucurbits worldwide and one of the most important diseases affecting these crops in Spain. Application of fungicides is the main control practice for managing P. xanthii; however, isolates resistant to multiple classes of site-specific fungicides have been recently reported in the Spanish cucurbit powdery mildew population. Succinate dehydrogenase inhibitors (SDHIs) constitute a relatively novel class of fungicides registered for powdery mildew control representing new alternatives for cucurbit growers. In the present study, 30 P. xanthii isolates were used to determine the effective concentration that reduces mycelial growth by 50% (EC50) to boscalid and fluopyram. The present study was also conducted to obtain discriminatory doses to monitor SDHI fungicide resistance in 180 P. xanthii isolates collected from several commercial cucurbit fields in Spain during 2017-2018. Three SDHI resistance patterns were observed in our population, which include patterns I (resistance to boscalid), II (resistance to fluopyram), and III (resistance to boscalid and fluopyram). The amino acid changes associated with these resistance patterns in the Sdh protein were also examined. Based on our results, SDHI fungicides are good alternatives for cucurbit powdery mildew control, although they should be applied with caution.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec