POP TIPS: sulfur sprays for peach leaf curl, brown rot, and fireblight

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Phil Forsyth

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Mar 26, 2015, 8:30:09 AM3/26/15

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WINTER/SPRING SULFUR SPRAYS FOR ORCHARDS

The application of sulfur sprays in late winter and early spring is commonly used for control of certain fruit tree diseases including peach leaf curl, brown rot, and fireblight. Although effective, sulfur is a drastic measure and should only be used as a last resort for for combating a disease in orchards. Even though it is accepted as an organic spray, it should be noted that sulfur is still toxic and should be used with proper safety precautions. Although it will not harm honeybees, it will kill a variety of both good and bad bugs as well as killing variety of good and bad fungi and other micro-organisms. For this reason, use sulfur only if a disease is having a dramatic effect on fruit production or tree health and other means of control have been ineffective.

Sulfur is naturally water insoluble. It is available in a dry powder form, but formulations termed 'wettable' or 'flowable' are generally best for orchard applications. Colloidal or micronized sulfur products are also preferred, as their smaller particle size is more effective in providing good coverage. {1}

When searching for a sulfur spray product you will also come across a lime sulfur compound. This will have the disease fighting benefit of sulfur with the added benefit that lime will allow for sulfur to penetrate the plant tissue, and thereby increasing its efficacy and faring better against rain or snow. This added benefit does come at a cost as the lime can damage the plant and the product is also more toxic than straight sulfur.

Safety precautions and spray directions

Sulfur spray is moderately toxic to humans and other mammals, so avoid direct contact and inhalation. When applying and mixing make sure to wear long sleeves and long pants, preferably of waterproof materials. Wear waterproof gloves and cover all other areas of exposed skin. Wear goggles and a dust mask. Never spray into the wind.

The focus of this POP tip is the use of sulfur sprays to prevent and combat brown rot in stone fruits (cherry, peach, plum, apricot); fire blight in apples and pears; and peach leaf curl in peach trees. For each application, please follow the directions on your packet for proper mixing proportions and spray the solution until all branches are drenched.{3} Sulfur spray should never be applied in temperatures above 85 degrees or if the temperature will exceed 85 degrees within 3 days of application. Also avoid use of sulfur spray within a month of oil spray applications. {2} Because sulfur can be corrosive to metals, sprayers with all plastic parts are preferable.

Sulfur Spray for Peach Leaf Curl

Peach leaf curl disease, scientifically known as Taphrina deformans, tends to attacks peach trees in humid climates. Sulfur spray can be used to kill the pathogens when the fungus is in the dormant stage. Late winter, meaning now, is the time to spray for peach leaf curl if it was a serious problem the year the before. For peach leaf curl, once the disease breaks dormancy for the season it is too late to spray. If you don't spray, the best means of control is removing infected leaves from the tree and any that drop to the ground.

A little peach leaf curl is not a big concern, but if your tree lost most of its leaves to this disease last season, a winter application of sulfur can help.

Sulfur Spray for Fire Blight

Fire Blight is a common bacterial disease of pome fruits, mostly spread in humid spring weather. Two prior methods to keep in mind for control of fire blight are to limit high-nitrogen fertilizers and to prune back 12 inches behind any sign of infection on branches. This emergency pruning should be done any time of year, as soon as you see any sign of the disease. If fire blight is an ongoing issue with pear, apple, or quince trees in your orchard, late winter is the time to spray sulfur while the fungus is in dormancy. In some locations, replanting with fire blight resistant cultivars may be necessary.

Late winter applications of sulfur can help reduce serious, ongoing problems with fire blight.

Sulfur Spray for Brown Rot

Brown rot is a fungal disease that effects stone fruit crops. Before spraying for brown rot, time and diligence should be taken to remove all infected fruit remnants from last year, both those still hanging on the branches and on the ground around the tree base. Another important preventive method is winter of pruning the tree to allow for greater air flow so branches can dry faster after ran events. Mulching at the tree base can also help, as the fungal disease can also be contracted from moist grass underneath the tree. To combat brown rot you can spray a lime sulfur spray during the dormancy stage; winter. In the early spring, you sulfur spray should be applied just before bloom and just after bloom. {E}