Organic Orchard Care: Monitoring for Pests and Disease in Spring

 A good time to do some monitoring and deal with early pests in the orchard is right after petal fall and as leaves emerge. 

Black cherry aphids

Aphids

Aphids can infect all fruit trees.  Different species affect different trees.They feed on the juices of plants.  Their saliva is toxic and causes curled leaves and deformed fruits. 

Host:   Apples, pears, peaches, nectarine, plums, and cherries

What to do:

As soon as the leaves emerge examine the undersides for aphids.  Look for the tiny pests at the base of the leaf.  They usually appear in clusters. Using a magnifying lens is helpful.   It is important to treat your trees before aphid feedings starts to curl the leaves. Once the leaves curl the aphids are protected from the sprays and much harder to get rid of.

After examining leaves from different levels of the canopy, if you see aphids you have a couple organic options:

•  Strong spay with a hose nozle to dislodge if infestation is light.  Repeat every 2-3 days
• Prune heavily infested sections if aphids infestation is small
• One of the following organic spray options
•  Insecticidal soap 
• 1% horticultural oil
• Neem Oil or
• Pyrethrin

Be sure to thoroughly cover the tree with the spray focusing on the undersides of leaves.  Horticultural oils and insecticidal soaps smoother the pest and must contact the aphid.

Types of Aphids

Apples are host to  rosy apple aphid and green apple aphid.  Green apple aphid is more common and populations begin to increase until the warmer summer months.  They remain in the orchard the entire season producing many generations.

The rosy apple aphid tends to be more of a problem in spring.  This aphid migrates out of the orchard to weed hosts in late June and July.

On peaches, green peach aphid is most common.  Their populations grow rapidly in the spring and cause distorted, twisted, and yellow foliage.  They eventually migrate out of the orchard in summer to weed hosts.

Plums and apricots suffer from mealy plum aphid and plum leaf curl aphid.

On cherries the black cherry aphid is the most common.  You can spot these on suckers at the base of the tree first. Black cherry aphids are easy to spot because of their color.

 Using a dormant spray when the sap begins to flow and buds start to swell is important in managing aphids.  This applications smothers overwintering eggs.  If you applied a dormant spray you should still check out your orchard early spring and look for aphids.

If you sprayed with a dormant spray acids may emerge  on only a few twigs and  you can prune those off to prevent spreading.

I f you have a large infestation an organic spray is best. After leaves emerge I use the following mixture in one spray application:

• Neem Oil
• Fish emulsion
• Kelp
• Repeat Neem or Horticultural oil if aphids are still a problem

For a heavy infestation if leaves have started to curl I use Pyrethrin.

Western Flower Thrips

Host:   peach, nectarine, apricot, and plum


If you had deformed fruit last year then you probably had thrips.  They are visible with a magnifying lens but easily overlooked with the naked eye.  Thrips feed on the developing fruit from bloom time til petal fall.


Organic option:  Spinosad  sold as Captain Jack's Dead Bug Brew

Spray in the evening.  When wet, Spinosad is toxic to bees but once dry it will not harm them.  One good application should work.

Apple Powdery Mildew

 Three conditions are necessary for a fungus to become active:  a proper host, specific weather conditions, and presence of the fungal spores.

The host for powdery mildew is apple and pears.  Powdery mildew is caused by a fungus that overwinters on twigs or a secondary infection when spores colonize a neighboring tree. New infections will reoccur if you had a previous infestation.  The fungal spores act as an inoculum and begin colonizing in early spring depending on weather conditions.  Powdery mildew can damage twigs, leaves, and fruit buds.

Begin monitoring for powdery mildew when buds are at tight cluster to open cluster or the pink stage. Look for mildew with a magnifying glass.  It is much easier to see.

If powdery mildew has been a problem treat 7-14 days after bloom with a sulfur spray.

Peach Tree Borers

Signs of peach tree borers are gummy exudates near the base of the tree and sawdust and frass where they bordered into the tree.

The borer larvae overwinter in the tree canopy.  In early spring, they emerge and feed on new foliage.  Once the shoots start to expand and grow they bore into the shoots.  

It is important to treat while the larvae are feeding on foliage.  After petal fall apply Bt (Bacillus thuringiensis). This bacteria must be ingested by the insect to be effective and is therefore is safe for bees.