Neem oil is a naturally occurring substance derived from the Azadirachta indica tree from India . Neem oil can also be used to control a wide range of insect pests organically , too . Additionally , biological control can be found by using a naturally occurring bacteria , Bacillus subtilis , which will prevent downy mildew from attaching to plant surfaces . Other fungicides available for the environmentally conscious include those containing baking soda and rhamnolipid ( a type of fat ) biosurfactancts that burst the cellular walls of mildew and other diseases naturally upon contact . As with any pesticide , remember “ the label is the law .” Use each fungicide in accordance with personal protective equipment ( PPE ), rates , and only on plants listed on the document included with each pesticide at the time of purchase . If you have lost the original label or it has become difficult to read , copies of product labels are required to be found on each manufacturer ’ s website .
Prevention
As with many diseases , botanical or otherwise , preventative measures are preferable to treatment . Whether plant selection or cultural practices , there are several strategies for avoiding downy
“ SOME DOWNY MILDEWS CAN SURVIVE COLD WEATHER ; OTHERS CAN BE CARRIED BY WIND AND INSECTS FROM
WARMER CLIMATES .”
mildews . While the weather cannot be controlled , the conditions favoring the formation of any mildew can be . Any planting area , new or existing , should be cleaned out to remove plant debris . Many types of spores can overwinter in field and garden debris and emerge from seemingly nowhere the following season . Some downy mildews can survive cold weather ; others can be carried by wind and insects from warmer climates . This means removing frost-killed vegetables from the previous year ’ s garden before planting new and clearing out fallen branches and leaves from around the landscape . New plants should be selected based on their resistance to downy mildew when such options exist . This information should be available on nursery tags at the garden or box store where they are being selected . Lists of downy mildew-resistant plants can be found from many reputable sources with a quick online search if there is no information on the tags . Certified root stock that is guaranteed to be free of downy mildew spores for onions , garlic , asparagus , and rhubarb should be selected if planning to grow these types of crops . Practicing crop rotation in the garden will help manage the spread of downy mildew as well .
Observe a three-year minimum rotation cycle for root crops to help avoid contracting any types of downy mildew that may be lingering in the soil . Delaying planting until after the threat of cooler , moist weather is another strategy . Existing plantings can be managed to avoid downy mildew formation as well . No matter how established your plants are , making sure there is enough airflow around them is critical to help avoid mildews and fungal problems of all kinds . For mature plants , make sure the lower branches and leaves are not laying on the ground . Keep all dead or damaged branches pruned out regardless of their location on the plant . Keep your plants trimmed back away from the house and other structures as well . For overly dense , but otherwise healthy plants , make some periodic thinning cuts to make sure there is good air circulation around them . This will help to reduce humidity around your plants and allow for better drying out of the foliage . Consider removing ( or transplanting ) mature landscape plants if they have grown too much into , or too close to their neighboring botanical friend . When planting new , consider spacing your selections based on the maximum spread listed on the tag so they do not grow into one another . Again , if this information is not readily available on the plant or nursery tag , there are hundreds to thousands of reputable plant databases online . Once the spacing and thinning issues have been addressed , consider watering practices . Too much moisture is one of the key causes of fungal issues including mildews . Since downy mildew develops in cool and moist environments , care should be taken when irrigating plants that may be susceptible to it . Watering should be done during the warmest part of the day or prior to it so that excess moisture has a chance to evaporate . When irrigating plants , try to keep all off the leaf surfaces , instead favoring the root zone and soil around the plants .
With such a range of practical and easily performed preventative strategies , downy mildew does not have to be a garden scourge . If you do , however , lose the battle on any of your plants , make sure to fully remove the plant and any fallen leaves or branches , and don ’ t allow them to decompose near your garden . Where possible , burn or otherwise dispose of plants that have been affected by downy mildew to help prevent its further spread or return .
36 Maximum Yield