New disease on apple trees

Spots and discoloration on the leaves of apple trees and premature leaf fall are caused by various pathogens. Most of these are apple scab or leaf spot diseases caused by fungi of the genus Phyllosticta . In recent years, home gardening and organic farming has more often seen a premature leaf fall in which the leaves had similar symptoms. According to investigations by the Bavarian State Research Center for Agriculture, however, the causative agent in these cases was not one of the known domestic pathogens, but the fungus Marssonina coronaria.

After a summer of frequent rainfall, the first spots may form on the leaves as early as July. They later converge and larger leaf areas turn chlorotically yellow. Also striking is an early onset of leaf fall, often in the summer. The fruits remain basically free from attack, but the leaf fall leads to a reduced fruit size and quality. The shelf life of apples is limited. In addition, next year is expected to lower flowering and fruiting.

The symptoms of fungal disease vary from species to variety. The leaves of 'Golden Delicious' show distinct necrotic grains, in 'Boskoop' the leaves are yellow in color and speckled with green dots. Idared, on the other hand, shows few symptoms. Interestingly, the strain 'Topaz' is particularly vulnerable, although it is quite resistant to apple scab, for example.

The home of Marssonina coronaria is Southeast Asia. The fungus can, like the well-known apple scab, overwinter on a fall foliage and the fungal spores infect the fully developed leaves after the apple blossom. Temperatures over 20 degrees and permanently damp leaves favor the infection - therefore the infestation pressure is particularly high in rainy years. Due to the possible climate change with increasingly humid summers, a further spread is likely, especially in home gardens, organic apple orchards and orchards.


Because the mushroom (Marssonina) overwinters during fall foliage, you should carefully collect it and promote a loose crown structure through regular fruit tree trimming, so that the leaves can dry well during the growing season. Fighting in the home garden with fungicides does not make sense, since the starting point for the hobby gardener is difficult to recognize and repeated spraying would be necessary for a sufficient effect. In conventional fruit growing, the disease is usually combated by the preventive scab treatments.

Why won’t Fuji apple tree bear fruit?

There are a variety of possible reasons why your Fuji apple tree is failing to bear fruit, including pruning techniques, variety and pollination.

If the tree has never bloomed, you may be pruning too severely. Most fruit trees require the development of spurs or short shoots on which flowers will form. It is important not to cut off all of the 1-year-old growth.

Allow dappled light to enter throughout the tree by thinning out crowded growth. Lack of sunlight can also prevent flowering and fruit set. In addition, avoid excessive heading cuts, especially during the dormant season, since heading encourages vigorous growth and reduces flower development.

If the tree has bloomed but has never set fruit, it may not be a Fuji or may need to have an additional pollinizer placed nearby to encourage bees and pollination. Although the Fuji cultivar should be "self-fruitful," meaning that it should not require cross-pollination from another apple cultivar to set fruit, it may be possible that the tree just needs additional help. Because it did have one instance of bearing fruit, perhaps a nearby apple cultivar in a neighbor’s yard helped with cross-pollination.

If the tree is not a Fuji or "self-fruitful," it will require a pollinizer (a tree or branch of a different apple variety with a similar bloom period) planted nearby (no further than 35 to 50 feet away). If there is no room to plant an additional tree, a pollinizer variety could be grafted onto the existing tree.

To test this solution, try placing flowering branches of a different pollinizer variety in a jar filled with water and set the jar in the tree canopy. Bees will visit these flowers and cross pollinate the existing tree.

When choosing a cultivar for cross-pollination, be sure that the bloom times overlap with the existing tree.

If the tree has bloomed and set fruit normally but the fruit dropped off prematurely, a variety of other factors could be causing poor fruit set, including the weather. During bloom time, strong winds and cold temperatures can greatly reduce or prevent adequate bee activity. Frost during or shortly after blooming can cause young fruitlets to abort even though no frost damage is seen.

Too much or too little water during the summer can cause fruit to drop. Drooping or yellowing leaves would indicate improper irrigation.

In addition, backyard fruit trees do not require heavy applications of fertilizer. Too much nitrogen will cause excessive new growth, which will shade out branches and cause poorer fruit set.

Depending on where the tree is located, it may be receiving too much shade from nearby trees or buildings or is competing for nutrients from other plants. Root constriction caused by hardpan or compacted soil, sunburn, borer insects, soil nematodes, root rot, powdery mildew and spider mites might also be affecting the tree. Take a close look and see if you can observe any other factors that might be impacting the tree’s health.

Tips For Planting Apple Trees

There's no more rewarding investment than planting trees. Apple trees that you plant early next spring may start yielding fruit in three to four years. But they'll be giving joy almost immediately. Planting trees with your children can be especially rewarding. They'll grow right along with your kids. A picture journal that begins at the first day of planting and continues through the years, with your kids standing right alongside their tree in each picture, will give you family memories that will last a lifetime, as will the tree itself.

Now you might be thinking that I'm jumping the gun here in late October. Nearly everyone recommends planting fruit trees in the spring, although you can get away with it in the fall if you have mild winters and protect the newly transplanted roots with plenty of mulch. But good organic tree-planting practice starts in the fall even if your trees won't go in the ground until spring. We went to the Maine Organic Farmers and Gardeners Association to find out more. Here is what they recommend.

Find a good location for your trees. Remember, unless you or your neighbor have nearby apple trees for pollination purposes, you'll need to plant more than one. Apple trees need as much sun as they can get. Don't plant them in the shade of a building or beneath other trees. The more air circulation a tree has, the less likely it is to develop blights and fungus. A slight slope where the air will "drain" downhill if it's cool is best.

Consider the soil. You should have a good two feet of loam to plant in even if the soil underneath is clay or otherwise hardpack. The next step is a familiar one: start a compost pile where you'll plant the tree. Break the soil up in an area a bit bigger than the size of a root ball. You might first want to first throw down some rock phosphate to give your newly planted trees the minerals it will need next spring.

Some gardeners recommend throwing down lime or a source of calcium but don't over do it. Apple trees like a slightly acidic soil — pH of 6.8 – 6.5 — though they'll tolerate anything close. Then start working in as much organic material as you can until you have a modest compost heap. When spring comes, the ground will have plenty of good stuff for your tree and it will be more easily dug. If you'd rather not start a whole heap, throw down some compost where the tree will be planted. Do it again in the spring. The more beneficial microbes inhabit the soil where a tree is planted, the less likely it is that the tree will have problems.

The other thing to consider is which type of apple to plant. Turns out the type of tree you stick in the ground goes a long way to determining the problems (or lack of) they may have. The best source of information for this is you local nursery or university extension service.