DIY Network

Diseases and Pests A guide to problems that can plague plum trees From "Fresh From the Orchard" episode DFFO-104

If you've ever seen white paint on the trunk of a fruit tree and wondered what its purpose was, you'll discover the answer here. You'll also learn how to protect a plum from pests and disease, how to thin small fruit in early spring and how to harvest perfectly ripe plums.

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Protecting Trunks From Cracking

Figure A

The trunks of plum trees, like those of many fruit trees, are susceptible to cracking in the winter. To prevent this, you can paint the trunk with white latex paint (figure A). Another option is to wrap the trunk with a paper or plastic truck protector (available from most nurseries) in the fall and remove the wrap in the spring.

Protecting Plums From Late Spring Frosts

A late spring frost can wipe out the harvest for a year. To protect against a frost that's predicted after fruit bud set, you can put lightweight plastic or fabric over the tree to form a tent and add a heat source in the form of a light bulb or a string of holiday lights. For safety's sake, use only UL-approved outdoor lighting and extension cords, and make sure that the light source doesn't touch the fabric and isn't too close to the tree trunk or branch, where it might burn.

If possible, plant trees on higher ground, since frost settles in low-lying areas. Sometimes an elevation difference of only 3' can affect the temperature by 5 degrees Fahrenheit.

Insects and Diseases

Plum trees are occasionally subject to pests such as the peachtree borer (figure B) and diseases such as brown rot (figure C). To minimize potential problems, select disease-resistant varieties and maintain good sanitary practices in your garden. Should you notice evidence of disease or pests, contact your local cooperative extension service for control recommendations. Your cooperative extensive service may also have a brochure that outlines a regular spray schedule if you live in a climate where that is recommended.

Figure B

Figure C

Cracking

	Figure D
	Figure E
	Figure F

Rainfall during harvest can result in a condition known as fruit cracking (figure D). Cracking is more of a problem for commercial growers because it makes the fruit unmarketable, but home growers can still pick and enjoy plums that crack during harvest. Just make sure you eat them before they begin to go bad.

Protecting Limbs From Breaking

The wood on plums trees tends to be brittle, and branches may break if a limb gets too heavy with fruit. Thinning will help, but for extra-heavy branches you may want to arrange a temporary support. For example, you can use a well-padded wooden prop to hold the branch up and take some of the pressure off the trunk or branch collar (figure E).

Harvesting

A big advantage of growing your own plums is that you can pick them at their peak of ripeness. Commercial growers are forced to pick plums before they are fully ripe so the plums won't rot during shipment.

All plums start out green but end up in a vast array of different colors (figure F). It's important to find out what the final color should be for the variety you're growing, so you'll know when to harvest the plums. As a general rule, you can tell if a plum is ripe by gently pressing it with your thumb. If the flesh is beginning to soften, the plum is probably ready to eat.