Healthy ap­ples keep the tree doc­tor at bay

Winnipeg Free Press - Section G - - HOMES - MICHAEL ALLEN

LAST week we dis­cussed a num­ber of is­sues that are caus­ing prob­lems for ap­ple trees. This ar­ti­cle will con­tinue with other is­sues faced by de­clin­ing ap­ple trees. Ap­ple scab is a fun­gal dis­ease that oc­curs mostly on or­na­men­tal crab ap­ple trees but can in­fect ap­ple trees as well. Ap­ple scab first ap­pears on the un­der­sides of young leaves in the spring as they open up and be­come tar­gets for in­fec­tion. The in­fected leaves be­come yel­low or or­ange-yel­low as they die, and then fall from the tree. The drop­ping of these pre­ma­ture coloured leaves is an im­por­tant symp­tom of ap­ple scab dis­ease. Dis­ease spots will show up on the leaves. The dis­ease rarely in­fects the fruit in Man­i­toba, but it does fur­ther south in the United States. Yel­low leaves are ac­tively drop­ping at the time of this writ­ing. This dis­ease can be con­trolled with the use of ap­proved cop­per sul­fate fungi­cide sprays, but these will need to be reap­plied af­ter pe­ri­ods of fre­quent rain­fall. At least two ap­pli­ca­tions will be nec­es­sary dur­ing the sum­mer. The treat­ment will need to be re­peated next year as well. Leav­ing dis­ease leaves around on the ground will re­sult in a re-in­fec­tion of the tree the fol­low­ing spring. All leaves, twigs and fruit must there­fore be col­lected be­fore win­ter and prop­erly dis­posed. I have writ­ten ex­ten­sively about fire blight dis­ease, how­ever, I con­tinue to find most own­ers of ap­ple trees are not aware of the signs of this dis­ease. Early signs of this bac­te­rial dis­ease in­clude in­fected flow­ers that have a brown­ish shriv­eled ap­pear­ance, shriv­eled leaves that turn a medium brown (of­ten cin­na­mon coloured in ap­ple trees), or curled ends of twigs with a dark brown or black (pear es­pe­cially) colour. Of­ten the in­side of the bark will be dis­coloured red­dish brown when the bark is peeled back on some trees. This is a lethal tree dis­ease and ac­tion on this must be taken right away if you want to try to get the dis­ease un­der con­trol. The dis­ease is of­ten trans­mit­ted by bees and wasps in the spring. Prun­ing off the in­fected parts at least 30 cen­time­tres away from the in­fected lo­ca­tion is very im­por­tant. Use sharp prun­ing tools and al­ways dis­in­fect the tools with bleach and wa­ter, or methyl hy­drate or with de­na­tured al­co­hol af­ter each cut. If this is not done the dis­ease will spread with the con­tin­ued use of prun­ing tools. Do not leave any pruned twigs or branches in the yard as the dis­ease will emerge in the fol­low­ing year to re-in­fect the tree. Fur­ther in­for­ma­tion about this dis­ease and il­lus­tra­tions are found in my new book, Dr. Tree’s Guide to the Com­mon Dis­eases of Ur­ban Prairie Trees. How­ever, the best time to prune healthy de­cid­u­ous (leaf shed­ding) trees such as fruit trees is nor­mally in Oc­to­ber or Novem­ber or in late March to early April. Cop­per sul­fate fungi­cide should be sprayed on the in­fected tree three times, ideally from mid-late May to July, about 10 days to two weeks apart. In­fected trees should be fer­til­ized ei­ther in the spring or fall to pro­vide nu­tri­ent energy to help re­pair dis­ease dam­ages. Ap­ple fruit is of­ten at­tacked by the ap­ple mag­got fly. The fe­male fly lays eggs on the newly de­vel­op­ing fruit in June. The eggs de­velop into mag­got lar­vae (grubs) which bore into the fruit leav­ing mushy brown trails in­side the fruit. Feed­ing by the mag­gots causes the ap­ples to fall.

The best way to con­trol ap­ple fly mag­gots is to trick them by us­ing red, sphere like Christ­mas or­na­ments. Match the size of the or­na­ment to the size of the fruit. Con­nect a good length of stiff (but partly flex­i­ble) wire to each or­na­ment. Then, ap­ply sticky Tan­gle­foot to at least five to seven red Christ­mas ball or­na­ments (ny­lon or plas­tic ones work well). Larger trees will likely need more or­na­ments. Sprin­kle the Tan­gle­foot with ap­ple cider pow­der or any fruit crys­tal essence. Be­gin the process once you see new fruit on the tree later in spring usu­ally about mid-June. Keep Tan­gle­foot away from your clothes and off your fin­gers. The sticky sub­stance will de­stroy clothes. Care­fully hang the balls from open branches such that if they were to move in the wind they would not make con­tact with other branches or leaves. Con­cen­trate more of the or­na­ments on the south side of the tree which is favoured by the flies. Check them fre­quently, clean the balls of in­sects, and re-ap­ply Tan­gle­foot. You will prob­a­bly have to do this ev­ery two to three weeks. It will not be prac­ti­cal to save the sticky balls for next year; so keep a sup­ply of the red or­na­ments for fu­ture use. When the fruit falls to the ground the mag­gots leave the fruit and bur­row about five cen­time­tres into the ground. In the soil, the mag­gots molt and be­come pu­pae. In the fol­low­ing spring the pu­pae change into adult flies, and the flies emerge from the ground in mid-June to early July. The growth cy­cle of the ap­ple mag­got is then re­peated. That is why one should never let in­fested ap­ples rot on the ground as the mag­gots do crawl out of the fruit. Those fallen ap­ples also at­tract wasps. Al­ways col­lect fallen ap­ples early and dis­pose of them in the trash or thor­oughly mix them in the com­post. Michael Allen M.Sc.F., RPF (ret’d) is a con­sult­ing ur­ban forester, tree di­ag­nos­ti­cian and cer­ti­fied ar­borist. He owns Vibur­num Tree Ex­perts. He can be

reached at 204-831-6503 or 204-223-7709.


Ap­ple fruit, above, is of­ten at­tacked by by the ap­ple mag­got fly. Feed­ing by the mag­gots causes the ap­ples to fall. Right, scab dis­ease

on a leaf.

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