Hello, My rental has a pear street tree, and the pears have black rotten spots at the blossom end, some look like they might have scab. Can you tell me what's wrong and if I can do anything to get a better harvest next season? Any idea what kind of pear?
Multnomah County Oregon
It appears that you have two problems going on. Scab a virus and codling moth an insect problem.
Cause Venturia pirina, a fungus that overwinters in infected fallen leaves and, in some areas, on pear twigs. Twig infection occurs sometimes in the Mosier and Medford, OR areas and commonly west of the Cascade Range and coastal British Columbia. Fallen leaves produce ascospores in the spring. Spores are generally released during rainstorms over a 3 to 4 month period but primarily during bloom. Infection occurs when leaves are wet for 10 to 25 hours and symptoms are seen in 2 to 3 weeks. Conidia are produced in these new scab spots and can infect healthy foliage or fruit.
The cultivars Forelle and Bartlett Red Sensation are very susceptible. The disease does not cause apple scab, nor can the apple scab fungus cause pear scab.
Scab on Asian pear is also caused by a different species, V. nashicola, that has not been reported in the Pacific Northwest. There are some reports of scab on Asian pear in the Willamette Valley of Oregon, but these have not been confirmed.
Symptoms In spring, sooty spots with a soft velvet look appear on young fruit, stems, calyx lobes, or flower petals. Young infected fruit frequently drop or are misshapen. Scab spots expand with growth until halted by dry weather or sprays. Old fruit infections often crack open. Cracks are surrounded by russeted, corky tissue and then an olive-color ring of active fungus growth. If fruit is infected late in the season, about 2 weeks before harvest, pinpoint-size scab spots often show up in storage a month or more later.
On leaves, olive-black spots expand with leaf growth but often cause the leaf to twist abnormally. Infected twigs show small blister-like infections the size of a pinhead and develop a corky layer. Many twig infections are sloughed off during the summer season.
Apply nitrogen (urea) to leaves in fall to enhance decomposition of fallen leaves and make them more palatable to earthworms.
Shred fallen leaves with a flail mower to help speed decomposition of infected leaves.
Pruning out infected twigs also offers some benefit.
Applying dolomitic lime after leaf drop in fall to increase soil pH also helps reduce inoculum the next spring.
A delayed dormant application is effective against twig infections in orchards that had a lot of disease the previous year(s).
BSP Lime sulfur (29%) at 6 to 11 gal/100 gal water. 48-hr reentry. O
Tetrasul 4s5 (27% lime sulfur) at 2.5 gal/100 gal water. 48-hr reentry. O
Use low-angle or microsprinkler heads, that do not let water wet fruit, under trees. Drip irrigation can also be used.
Reduce the length of irrigation sets.
On apples and pears, larvae penetrate into the fruit and tunnel to the core, leaving holes in the fruit that are filled with reddish-brown, crumbly droppings called frass (Figure 6). If left uncontrolled, larvae can cause substantial damage, often infesting 20 to 90% of the fruit, depending on the variety and location. Late maturing varieties are more likely to suffer severe damage than early varieties.
Codling moth can be very difficult to manage, especially if the population has been allowed to build up over a season or two. It is much easier to keep moth numbers low from the start than to suppress a well-established population. In trees with low levels, codling moth often can be kept to tolerable levels by using a combination of nonchemical management methods; however, it is important to begin implementing these measures early in the season.
Where populations are moderate to high and many infested trees are nearby, insecticide applications might be necessary to bring populations down to low levels. To be effective, the timing of insecticide spray applications is critical, and several applications are necessary, especially with newer, less toxic pesticides. In most backyard situations, the best course of action might be to combine a variety of the nonchemical and/or low toxicity chemical methods discussed below and accept the presence of some wormy fruit. If eating wormy fruit, be sure to cut out damaged portions, because they might contain toxins (aflatoxin) generated by mold. It is ideal to make codling moth management a neighborhood project, because your trees can be infested by moths from your neighbor’s trees, despite your own best efforts at keeping populations of this pest down.
Hope this helps!