Peach diseases and pests- do you know know your enemy?
Several fungi (moldy things) and some bacteria attack peach crops. Various fungal problems start as the flowers open and continue all summer and through harvest. Fungus causes wilted flowers, obvious rotten spots, scabs or mold growth on fruit at various stages, oozing cankers (sores) on twigs, or curled, shriveled, or discolored leaves. There's also a bacterial disease that can make spots on peach leaves or fruit, or can cause the tree to lose leaves which in turn makes the tree unable to produce really tasty big peaches.
A medley of moths, beetles, mites, scales and hoppers can attack just about any part of your peach tree. Some bugs are easily found as they attack the fruit or leaves of the peach tree. Others are more furtive but their damage shows as sappy holes in the tree trunk, sawdust, dead leaves on twigs and small cuts or wounds on the fruit.
Questioning the spray
The many hazards to peach tree health lead peaches to be one of the more chemically treated commercial fruit crops. News stories and medical studies have many of us worried over the safety of "sprayed" crops. As gardeners, we also worry about our personal safety if using garden chemicals. With those issues in mind I questioned whether amateur owners of backyard peach trees could produce an "organic" peach harvest.
Growing a thriving peach tree in a clean environment helps reduce (but almost surely will not prevent) problems. Start with good soil and a properly chosen peach tree for your area (consult recommendations from the closest university or arboretum.) Prune and fertilize the peach according to recommended advice and schedules. Publications from University of Georgia (linked here) give comprehensive guidance for those cultural concerns. Learn about the insects and diseases that are of particular concerns in your area. For example, California peach growers face far fewer fungal threats than those in Georgia. Keep peaches well watered.
Keep the area under the trees mulched and clean of any debris. Paint the tree trunk with diluted (1:1 paint/water ratio) white latex paint to avoid peachtree borers. (Note that method is not currently "certified organic" but I'm sure a backyard gardener is comfortable with using the product.) Remove dropped fruit; it may have fallen due to infestation. Carefully observe your peach for all signs of problems. Assume that any insect you see in large numbers on your peaches is a problem. (As analogy, think of a herd of antelope and one lion. Predatory insects, the lions in the analogy, are usually scattered and mobile as they hunt for victims.) Treat problems quickly. Be especially vigilant in removing any suspicious, possibly diseased plant parts. Handle ripe fruit gently to avoid bruising it. If you are happy with SOME peaches from your tree this may work for you.
If problems arise
No research links that I found would guarantee success with simple fastidious care. If, I should say when, problems do arise, treat quickly. There are treatment choices which reduce toxic loads to you and your environment. The following products have fair to good results on certain fungus and insects. Use the products regularly, as directed, and never assume one single treatment will eliminate a particular pest or disease.
Lime-sulfur is traditional yet effective fungicide. It's an elemental solution approved for use in organic orchard operations. You mix the solution and thoroughly spray the tree; drips and excess spray product simply degrade into calcium or sulfur compounds naturally found in soils. Lime-sulfur is approved for use in registered organic operations. It is used during the winter to suppress or prevent fungus, and can be sprayed in more dilute form during the growing season to treat fungus. Search online for sources if you don't find it locally.
SurroundWP™pesticide contains superfine clay (kaolin) particles. Surround is mixed with water and sprayed, forming a very thin but fairly effective insect barrier on all surfaces on leaves and fruit. Surround seems a bit pricey in homeowner size five pound (makes ten gallons) pack. You might wish to invest in a 25-pound bag.
Spinosad is a relatively new pesticide derived from soil organisms. It's effective against certain insects in the larval stage. Spinosad is listed as an active ingredient in some pesticides labeled as organic or eco-safe.
B.t. is also an effective, organically approved, insecticide but only toxic to certain insects in their caterpillar phase. Check product information for B.t. content and recommendations. Dipel is one B.t. product for peach tree care.
With the list of effective yet "organic" treatments so short, pyrethroid pesticides may be worth your consideration. Pyrethroids are man-made versions of the plant extract pyrethrin which is a safe plant extract. Pyrethroids are made with petroleum derivatives and are more persistent and effective than basic pyrethrins. But pyrethroids are lower in toxicity to people, birds, and most mammals than the worst of the worst , the organophosphate insecticides . Note: pyrethrins and pyrethroids are toxic to cats, bees, fish, and amphibians.
All of these products come with their own set of user cautions and recommended dilutions. Educate yourelf about these treatments and read and follow label directions. A number of other products or treatments appeared in the articles I consulted. However, beyond what I have just listed, the products were either of very limited effectiveness, or I was unable to find the product available to homeowners at this time.
I hoped for a rosier organic outlook for backyard peaches. After studying growing advice and product availibilty, it seems a home grower of peaches has few options which both guarantee peach production and leave total peace of mind regarding chemical use. Peaches are simply not a beginner fruit crop, especially in humid environments. Growers of organic peaches really earn their money. Researchers have been working, and continue to strive for, the best techniques in peach cultivation with the lowest chemical exposure at all stages. I really can't do justice to the entire topic of peach care here; please see the resources below for more information.
(Most of all I wish us both luck with our pet peach trees because we are going to need it!)
Endnotes and Resources
1 Pottorff, Laura. "Some Pesticides Permitted in Organic Gardening."published 01 / 05/2010. Colorado State University Cooperative Extension. accessed May 10 2011. < http://www.colostate.edu/Dept/CoopExt/4dmg/VegFruit/organic.htmSome Pesticides Permitted in Organic Gardening>
2. Diver, Steve and and Tracy Mumma. "Organic and Low Spray Peach Production." 2003. ATTRA - National Sustainable Agriculture Information Service. accessed May 10 2011,<http://attra.ncat.org/attra-pub/peach.html>
3. Horton, Dan, John All, and Dean Kemp. "Home Orchard Insect Pest Management Guide", and "Home Fruit Insecticide Effectiveness Chart" and Little, Elizabeth. "Home Orchard Peach, Nectarine and Plum Disease Spray Guide." all from the Homeowner Edition of the Georgia Pest Management Handbook.<http://www.ent.uga.edu/pmh/Hm_Fruit&Nuts.pdf>
4. Taylor, Kathryn C. "Home Garden Peaches and Nectarines." 8/ 1/ 2008. University of Georgia. accessed May 10 2011. < http://www.caes.uga.edu/publications/pubDetail.cfm?pk_id=6365>
5. The Organic Materials Review Institute <http://www.omri.org/>
Site allows search for products or materials by name and lists some sources of organically acceptable products. accessed May 10 2011.
"The Organic Materials Review Institute (OMRI) is a national nonprofit organization that determines which input products are allowed for use in organic production and processing. OMRI Listed-or approved-products may be used on operations that are certified organic under the USDA National Organic Program. OMRI's funding comes from a variety of sources, including sales of publications, grants, donations, and subscriptions. Mainly, however, the organization generates income through fees collected for the review of products intended for use in organic production or processing. Also, OMRI operates an organic seed information service to help growers find organic seeds. "
6. Fishel, Frederick M. "Pesticide Toxicity Profile: Synthetic Pyrethroid Pesticides." Florida Cooperative Extenstion Service. 7/ 2005, reviewed 9/ 2008 and 4/2011. University of Florida. accessed May 10. 2011. <http://edis.ifas.ufl.edu/pi091>
7. Knutson, Allen et al. "Homeowners Guide To Pests of Peaches, Plums and Pecans." Texas Cooperative Extension. 5/05. Texas A & M. accessed May 10 2011. <http://www.plantanswers.com/homeowner_peach_guide.pdf>
And two suppliers--not a business endorsement but they do have information on the named products also.
Dirtworks, supplier of a range of organic products
Gardens Alive, mail order source "dedicated to biological control of garden pests. "