Eat Your Lima Beans, They are Not Moldy

Lima Beans: the Good, the Bad, and the Edible.

Lima Beans: moldy (L); Fungicide Treated (R)

Lima bean has been an important crop grown for canning and freezing in the mid-Atlantic area of the United States since the nineteenth century. Lima bean grown for processing is planted on 6,500 hectares in Delaware, with production valued at $6.5 million. 13,000 hectares of lima bean are grown in the United States, with California being the largest producer of lima bean and Delaware being second. Lima bean is considered to be the cornerstone crop of the vegetable processing industry in Delaware, and Delaware remains one of the few states that produce the crop. Lima bean downy mildew was first reported in Connecticut in 1889, and the disease is in Delaware almost every growing season.

“Currently, P. phaseoli [lima bean downy mildew] is limited to the mid-Atlantic areas of Delaware, Maryland, and New Jersey and has never been reported to occur in California. This is likely to be due, at least in part, to California’s lower humidity compared with the eastern United States.

In 1958, P. phaseoli was responsible for an epidemic, with more than 907,185 kg of bean loss from 4,725 hectares in Delaware. In 2000, race E of P. phaseoli was responsible for an epidemic in Delaware during September and October, which resulted in an estimated production loss of 40%, equal to a farm value loss of $3,000,000.

Fungicide testing for control of downy mildew of lima beans began as early as 1897 when Bordeaux mixture was recommended for control.

Growers currently make preventative applications of copper fungicides either alone or in combination with insecticides for pod-feeding insects. When conditions for downy mildew are favorable and outbreaks occur, applications of Ridomil Gold/Copper (mefenoxam) or Phostrol are made curatively to unsprayed fields or those where copper fungicides have been applied preventatively.

Currently, several fungicides are labeled and effective for control of downy mildew if applied in a timely manner. Ridomil Gold/Copper (mefenoxam/copper), Phostrol (phosphorus acid salts), and copper fungicides are currently labeled on lima bean and are effective.”

Authors: Evans, T. A., et al.
Affiliations: Department of Plant and Soil Sciences, University of Delaware.
Title: Lima bean downy mildew: impact, etiology, and management strategies for Delaware and the mid-atlantic region, U.S.
Source: Plant Disease. 2007. 91[2]:128-135.

New Fungicides Take the Worry out of Controlling Mildew on Lettuce


Lettuce Downy Mildew

Downy mildew is a common fungus in most lettuce growing regions, especially during cool, moist weather.  Spores can be blown long distances.  Under favorable conditions, downy mildew is a very explosive disease, capable of appearing at high incidence in a field overnight.  When spores land on lettuce foliage, they germinate and can penetrate the lettuce leaf within three hours.  Lettuce is susceptible at all growth stages to the downy mildew pathogen.  Following penetration and establishment in the leaf, fruiting stalks grow through the leaves and branch repeatedly producing several spores on each tip, resulting in a whitish mat of millions of spores on each plant.  Affected tissues turn brown.  The fungus can penetrate to leaves internal to the wrapper leaves.  Relatively low levels of infection can downgrade a crop, cause significant trimming losses at harvest and promote decay by bacterial organisms during postharvest transport and storage.  During transit, lesions become soft and slimy as secondary decay organisms gain entrance through the tissues infected with the downy mildew fungus. High levels of disease can render a crop unmarketable.

“Incited by the obligate parasite Bremia lactucae, downy mildew is one of the most devastating diseases of lettuce worldwide. Attempts to manage this fungal disease using host-plant resistance have frequently failed due to the development of new races of the pathogen. Therefore, chemical control is of the utmost importance in humid areas where environmental conditions are very favorable for disease development.

Since the year 2000, a number of new fungicides targeting the Oomycetes, the class of fungi to which downy mildew belongs, have come to the market or are being considered for registration. It was the objective of these studies to investigate a select number of these for potential use in Florida for lettuce downy mildew control.

Of those investigated, mandipropamid and fenamidone consistently provided for high levels of control. Fluopicolide, dimethomorph, dimethomorph plus ametoctradin, cyazofamid, and propamocarb also provided significant control. With the majority of these fungicides already being labeled or close to being labeled on lettuce, it would appear that lettuce growers now have a wide array of efficacious downy mildew fungicides with differing modes of action from which to choose. This is a far cry from the situation that existed during 1989, when the EBDC fungicides were being threatened with cancellation and metalaxyl insensitivity was becoming widespread.”

Authors: Raid, R. N., and D. D. Sui.
Affiliation: University of Florida, IFAS, Everglades Research and Education Center.
Title: Management of lettuce downy mildew with fungicides.
Source: Proc. Fla. State Hort. Soc. 2012. 125:218-221.

Downy mildew of Basil is here to Stay

Downy Mildew Close-up

Downy Mildew Close-up

Downy Mildew Spore Growth on Basil Leaves

Downy Mildew Spore Growth on Basil Leaves

Downy mildew of basil is a new destructive disease that appears to be here to stay. In the first years of its appearance in the U.S., complete crop losses occurred for some growers because basil leaves with any mildew are unmarketable. Applying fungicides frequently and starting before first symptoms are considered necessary to control basil downy mildew effectively.

“Sweet basil (Ocimum basilicum L., Fam. Lamaiaceae) is the most commercially important annual culinary herb crop grown in the United States. Sweet basil is grown for culinary use for both fresh and dry consumption and as a source of essential oil and oleoresin for manufacturing perfumes, food flavors, and aromatherapy products.

Basil downy mildew… is a new disease of basil in the United States. …In the United States, the pathogen was first discovered in Florida in the fall of 2007. Since that time, basil downy mildew has been found throughout the eastern United States and in regions of commercial basil production in the Midwest and California.

Once basil plants become infected and develop symptoms, they are no longer marketable as a fresh product. …Currently, there is no known resistance or tolerance to basil downy mildew leaving 100% of the sweet basil acreage in the eastern United States vulnerable to the pathogen. Without adequate chemical control options and genetic resistance, basil downy mildew has the potential to destroy basil production in the eastern United States and in all other areas where basil is being produced.

Selection criteria such as foliar morphology, plant architecture as well as the presence of secondary metabolites and other factors that provide a less favorable microenvironment to the pathogen need to be examined as potential avenues for developing downy mildew-resistant sweet basil cultivars. Until this can be achieved, basil growers will have to rely on multiple applications of the few commercial fungicides currently registered to produce a marketable crop. Additionally, for organic basil growers, control of basil downy mildew will be even more challenging because there are fewer approved products labeled for organic use.”

Authors: Wyenandt, C. A., et al.
Affiliation: Department of Plant Biology and Pathology, Rutgers University
Title: Susceptibility of basil cultivars and breeding lines to downy mildew (Peronospora belbahrii)
Source: HortScience. 2010. 45(9):1416-1419.