What are the major pests and diseases in peach trees, and how to control them
Unfortunately, peach trees suffer from various fungal and bacterial diseases and various pests. The farmer should visit his/her orchard often and observe the trees for any early symptoms that could indicate the presence of a pathogen or a pest. The use of traps for monitoring key pest populations may be necessary in some cases. In general, the use of preventive strategies and not only control management has greater benefits for the environment, the trees, and the farmers since it can reduce the total cultivation costs and allow the building up of a healthy population of beneficial organisms (natural enemies of crop pests). Some of these practices are proper weed control, pruning, and training for improved aeration of the tree canopy, etc.
On the other hand, many farmers apply a series of applications with insecticides or/and fungicides routinely without having any evidence of the presence of an enemy or symptoms (damage). However, despite the short-term efficiency of this practice, it has quite high economic costs, an increased risk of resistance development of pests and pathogens to the substances used, and the elimination of beneficial organisms in the orchard. Before applying any control measure, it is best to consult your local agronomist and adjust your practices based on the year and region (environmental condition), the peach variety and the age of the trees as well as the type-species of pests and pathogens (you may have to keep records of previous years). Remember: It is vital to take all safety measures when applying pesticides and fungicides (protective clothing, following the instruction on the product’s label, respecting the minimum amount of days from the last application to the fruit harvest, etc.).
The most important pests of Peach trees
Oriental Fruit Moth
The Oriental fruit moth is the most common and damaging pest of Peach trees but can infest other fruit trees as well. The insect Grapholita molesta (Order: Lepidoptera) causes severe damage to fruits due to the activity of the larvae that feed and open holes in them. These damages dramatically reduce the commercial value of the fruits that are unsuitable for the fresh market (and usually for the industry as well). The farmer may observe scattered deposits of thick sap (gum) and frass on the skin of infected peach fruits. Except for the damage caused in peach fruits, the insect can infest the shoots and cause tip wilting and stunt growth.
The peach farmer should remove by pruning and destroy the infected plant parts by cutting at least 6 inches (15 cm) below the damaged area. In small orchards or for trees grown in a garden, it is also possible to kill the larvae by entering a wire in the holes of the stems.
Borers (Peach Twig Borer and Greater Peach Borer)
These pests are a major problem for peach trees and nectarines but can also be for other crops like apricots and plums. The damage is caused by the larvae that create tunnels on the trunk (at the cambium close to the soil line) or the branches and shoot tips (depending on the species). The farmer may observe oozing tree sap (gum) mixed with frass coming out from the tunnel opening, dead twigs/shoots, holes in fruits (from the Peach Twig Borer), or wilting shoots and holes in stems’ ends and on ripening fruits.
In years that the chemical control of the insects is necessary, the (conventional) grower may spray with permethrin or carbaryl in early summer on the trunk close to the ground or the canopy (pyrethroids and malathion). You should always consult your local licensed agronomist. In organically cultivated peach orchards, growers may use spinosad, beneficial nematodes (for the Crown Borers), and Bacillus thuringiensis (for the Peach Twig Borers) products. Keep in mind that the species and population (damage) of pests may differ from one region to another and yearly.
Peach Diseases (Identification and Management)
Brown Rot
Brown Rot, caused by many different species of Monilinia (such as M. fructicola, M. laxa, M. fructigena), is the most destructive disease of Peach trees. The fungus infects flowers, young shoots, and mature fruits, causing twig canker, branch dieback, blossom blight, brown lesions, and shriveling up of the fruits and, as a result, a significant decrease in fruit yield. The phytopathogenic fungus is widely spread and a major problem for peach growers in Europe, North and South America, and Asia.
The farmer should apply proper weed control, plant the trees at safe distances, ensure proper drainage and avoid foliar irrigation. Diseased twigs and mummified fruits should be removed from the tree and the field ground. The general condition of the plants (nutrition and water availability, sun exposure) can also boost their resistance. It is also crucial to use proper sanitation, such as tools disinfection every time we touch the plants. Moreover, all diseased, mummified fruits and branches should be removed from the field and destroyed. Chemical treatment (2-3 fungicide applications during flowering and petal fall) is an efficient control measure. Still, it should use only if the problem is severe (in areas with known disease history) and always under supervision from a local licensed agronomist. For such applications, the farmers can use airblast sprayers (for larger orchards) or handgun sprayers. Green fruits are not susceptible to new infections.
Powdery Mildew
Sphaerotheca pannosa causes extensive damage to peach trees and other stone fruits. We may observe chlorotic spots on infected plants with a characteristic whitish powder resembling flour on leaves, stems, flowers, and green fruits. Sometimes, on the fruits, these spots take a red-purple color covered by the characteristic powdery white coating.
Management of the disease includes the same measures as other fungal infections.
Leaf Curl
Leaf curl is a disease caused by the pathogen Taphrina deformans. The fungus infects peach trees causing intense leaf curling and red discolorations, mainly on young, newly developed leaves. If the infection is severe and left uncontrolled, total defoliation of the tree may occur. Management of the disease includes the same measures as other fungal infections. Usually, it consists of a program of 3 sprays with suitable fungicides (1 during leaf fall, one before budswell, and one week later). However, you should always ask first your local licensed agronomist.
Shot Hole - Bacterial spot
The Bacterial spot is a disease with significant economic costs caused by the pathogen Xanthomonas arboricola pv. pruni, which can also infect apricots, cherries, and almonds globally. As the name of the disease reveals, symptoms include dark spots resembling gunshots on the leaves, stems, and fruits, decreasing their commercial value. The initial symptoms are usually water-soaked lesions that expand, and finally, they dry out and abort. Later in the season, small brownish lesions may appear on the infected fruits and can serve as a source for secondary infections after the pit hardening stage.
References:
- https://extension.umd.edu/hgic/topics/diseases-stone-fruit
- https://fdc.nal.usda.gov/fdc-app.html#/food-details/341586/nutrients
- http://www.opengov.gr/ypaat/wp-content/uploads/downloads/2013/02/rodakinia_nektarinia2.pdf
- https://www.aua.gr/roussos/Roussos/pdf/Printing%20Lessons/EFP6/Peach%20vF%202019.pdf
- https://extension.psu.edu/peach-production
- https://extension.uga.edu/topic-areas/fruit-vegetable-ornamentals-production/peaches.html
- http://www.geotee-anmak.gr/img/ekdiloseis/pyrinokarpa_3.pdf
- https://www.rdos.bc.ca/assets/PUBLICWORKS/Pest-Management-Control/Tree-Fruit-Bush-and-Berry-Pests/Peach-Fact-Sheet.pdf
- https://phytopatholres.biomedcentral.com/articles/10.1186/s42483-022-00134-0
- https://extension.umd.edu/resource/peach-cherry-plum-and-nectarine-insect-pests
- https://agriculture.vic.gov.au/biosecurity/plant-diseases/fruit-and-nut-diseases/stone-fruits/peach-leaf-curl
- https://extension.usu.edu/pests/ipm/notes_ag/fruit-list-peach
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