Apple Trees Looking a Little Rusty?
WD40 won't help you fight the dreaddisease they call Rust
Question. Every spring our ornamentalcrab apple tree is infested by a rust that ruins the leaves and causesthem to dry and shrivel in the summer. I am aware that these trees needto be sprayed with an oil-based solution immediately prior to budding,but this has not worked in the past. I have also been told thatsuppository-like things can be drilled into the tree or put into theground during the fall to prevent the problem. Any other suggestionswould be appreciated. The tree looks terrible most of the springand summer months.
----Nancy in Media, PA
Answer. Yes, rust really does liketo go after apple trees—both fruit bearing and ornamental types likeyour flowering crab apple—big time. It generally shows up late in theSpring, in the form of pale yellow spots that gradually get bigger andtake on that familiar orangey color.
The answer you always hear is to remove any nearby cedartrees—especially Eastern red cedar—and, less frequently, other membersof the Juniper family (yes, cedars are junipers—plants have familiesevery bit as confused as yours). There are a number of different'species' of spore-borne fungal diseases grouped under the general name'rust'—another well-known one loves to attack roses—but this type needsto also grow on cedars (or other junipers) before it can infect appletrees (that's why its common name is 'cedar-applerust'). And it's far from the most complicated kind—one type ofrust has to 'jump' to five different types of plants in a season tocomplete its life cycle. Kind of like that bug the kids brought homefrom school for your Christmas present.
Anyway, the spores can overwinter in debris on the ground (which makesa good clean-up underneath the tree in the Fall essential), and/or theycan spend the off-season on cedars and junipers, which I'm now justgoing to pretend are two different things so I don't have to insertfamily tree explanations into the dialogue every time I mention thedang things. On cedar and junipers, the disease takes the shape oflarge, soft galls on the branches that, like teenagers, develop longcolorful horn-like structures when the weather warms up. Those hornsthen spit out disease spores that go looking for your floweringcrabapple—their hands-down favorite victim. (If you ever see thesekinds of structures on your cedars or junipers, prune them off andtrash them—even if you don't have apple trees; you might be ending therusty misery of an apple grower miles away!)
If you've got an apple tree planted close to a cedar or juniper, it'llnever be happy till one or the other goes bye-bye. But rust may stillcome a callin' even if you do get rid of any cedars and junipers closeby. Those rusty spores can travel up to four miles on a windy day, andyou may never even see the playmate that's making your plant sick.
That's why you should make your apple trees as resistant to the problemas possible:
1) Clean up EVERYTHING underneath the tree after theleaves drop in Fall. Really rake that ground hard, and throw all thedebris in the trash—don't compost it.
2) Then spread an inch of your best qualitycompost underneath the tree as far out as the furthest branchesgo—the living creatures in that compost will eat any disease spores youmissed.
3) Don't use chemical fertilizers. The weak unnaturalgrowth they cause is especially prone to this problem—and otherdiseases.
4) Prune the tree to increase air circulation. Thebook says to do this right now—in the middle of winter. But that'llcost you a lot of the flowering display that's the only reason you'rekeeping the furshuligner thing around to begin with. So make yourpruning PLANS now. Take a good look at the thing while it's bare, andmark what you plan to remove as soon as the flowers are done showingoff. Open up the center, and remove crossing branches to improveairflow into the tree. If you can't do this safely by yourself, hire aprofessional. (MEN!!!: I'M TALKING TO YOU!!!! "HELLoooo…" )
5) And if the entire area has become overgrown, prunenearby plants to improve airflow to the tree as well.
6) Then immediately spray the tree with composttea, fermented compost tea or oxygenatedcompost tea, and repeatthe spraying weekly till you're past the season of rust. This will putbillions of disease-eating guys right where the spores will belanding—and provide a nice foliar feeding your tree will really enjoy.
7) Forget those oil sprays you mentioned. They'rebest used controlinsect pests—not disease. And I don't even want to touch your'suppository suggestion'! Instead, watch carefully for the first signsof discoloration, pick off any infected leaves you can reach, andimmediately spray the entire tree with sulfur or copper.
8) Research has also shown soap sprays to beeffective against rust, and at least one product combines copper with afungicidal soap—Gardens Alive "soapshield". (I'm gonna sneak on their web site some night and changeall these cutesy names before they give ME one.) I especially like thatthis stuff contains a lot less copper than a regular copper-alonespray, which is good. With copper or sulfur, you always want to use thesmallest amounts possible.
9) Oh, and if you're planning to grow apples foreating, plant types that naturally resist rust and go home early. Thisincludes such popular varieties as "Stayman", "Empire", "Gala","GrannySmith" and "McIntosh"
You Bet Your Garden Question of the Week ©2005 MikeMcGrath