Pear scab
Venturia pirina
What is Pear scab (Venturia pirina)?
Pear scab, caused by the fungus Venturia pirina, is a worldwide fungal disease that primarily affects pear trees in temperate regions. It infects leaves, fruit, and young twigs, causing circular lesions ranging from olive green to dark brown to black. Initially velvety, the lesions later become cracked and corky. Fruit lesions measure approximately ⅛ inch in diameter, while leaf lesions are about 3/16 to 3/8 inch in diameter. Their irregular and diffuse margins differentiate them from other common spots on pear foliage.
How does a Pear scab (Venturia pirina) occur?
Pathogens overwinter primarily in infected leaves on the ground. In spring, primary spores (ascospores) are carried by air currents or splashing water to flowers, leaves, or fruit, causing initial infections. In high rainfall areas, the pathogen can also overwinter in twig lesions. Secondary spores (conidia) are produced on infected leaf or fruit surfaces, spreading the disease until conditions become dry, or the plant tissue becomes more resistant. Infection occurs rapidly between 55° and 75°F, with continuous wetness of at least 9 hours needed for initial infection at these temperatures.
Symptoms
1 - Plants Health
• Pear scab can cause fruit to become malformed, cracked, and unsightly, rendering it unusable. Severe early leaf infection can lead to defoliation, impacting the overall health and vigor of the tree. • Continuous infections of pear scab can weaken the plant's natural defense mechanisms, making it more susceptible to other diseases and pests.
2 - Impact on Soil
Pear scab can affect the decomposition rate of infected leaves, potentially impacting nutrient cycling in the soil.
Solutions
1 - Cultural Control Measures
• For backyard trees, remove and compost or destroy fallen leaves in autumn to limit disease levels. • Apply zinc and fertilizer-grade urea (or nitrogen source) to leaves in autumn to hasten leaf fall. • Add lime to leaf piles beneath the tree to reduce overwintering inoculum. • Choose pear cultivars with resistance to pear scab and other scab-resistant varieties. • If using sprinklers, irrigate between sunrise and noon to allow adequate drying time or adjust the angle of the sprinkler.
3 - Application of Fungicides
• There are several fungicides available for controlling pear scab, including propiconazole, myclobutanil, tebuconazole, and copper-based fungicides (such as copper octanoate and Bordeaux mixtures) sulfur, mineral oil, and neem oil. • It is important to carefully follow the instructions on the fungicide labels for proper usage, application rates, and safety precautions.
4 - Biological fungicides
• Biological fungicides for controlling pear scab include Bacillus subtilis, Trichoderma spp., Serenade® Garden, and Regalia®. • These products harness the power of beneficial bacteria or plant extracts to combat fungal diseases in an environmentally friendly way. • It is important to carefully follow the instructions on labels.
