Before an orchard is replanted, the soil should be ripped and cross ripped to a depth of two to three feet and fumigated.
Good site preparation can make a huge difference to the financial success of a new orchard planting, and there’s only one opportunity to do it—before the trees are planted, Tim Smith, Washington State University Extension educator, said at a recent Fruit School on Competitive Orchard Systems.
Before replanting an orchard, the grower should consider the physical, chemical, and biological aspects of the site, Smith said.
When orchards were planted less intensively, trees were usually planted in individual, augured holes that were filled with new soil. It was a laborious and time-consuming process that didn’t work very well, Smith noted. The soil outside the planting hole was quite different from the soil in the hole and much more compacted, and the tree roots tended to stay in a ball in the softer soil in the planting hole rather than try to drill into the compacted soil.
With higher density plantings, it’s more practical to prepare the whole site ahead of planting. The soil should be ripped and cross-ripped to at least two feet in depth, and ideally three feet, Smith said. The ground should be just as well prepared as if the grower was about to plant potatoes, not trees. Trees have two years to establish a good root system before the replant organisms return. If they get off to a good start, they’ll keep growing well. If not, they’ll suffer for the rest of their lives with a limited and ill root system. "Give those roots as good a chance as possible to grow," he urged.
The soil should be analyzed at least a year ahead of planting so that corrections can be made to nutrients or the pH level after the old orchard is removed and before the new one is planted. Don’t just check the top foot, Smith cautioned. Check the second and third feet.
If the pH level is below 6, lime can be added to stop it dropping further. The lower the pH level, the faster it will drop, Smith warned.
In most orchard sites in central Washington, it’s rarely necessary to add potassium, but there are a few cases where it is lacking. It’s good to correct it while the trees are young because potassium applied to older trees can cause bitter pit.
If phosphorus is low, this is a good time to add that, too. Phosphorus is not very mobile in the soil, but if it’s applied before planting, it can be stirred into the soil.
Concerning zinc and boron, Smith said he has seen situations where, if the orchard site was left fallow for two to three years, zinc and boron became tightly bound in the soil, which led to a deficiency in the young trees. Symptoms of a boron deficiency are cupped, boat-shaped leaves. A distinctive symptom is shoot dieback with a proliferation of shoots growing at the base of last year’s shoot. Deficiencies can quickly be corrected with nutrients. Lime and nutrients can be worked into the soil after it’s been ripped.
The biological issues are the most important to consider when replanting, Smith said.
If there are ten-lined June beetle larvae in the ground, they will chew all the roots off young trees except for those that are bigger than pencil size, he warned. The trees don’t die, but they don’t grow. The pest is most common in dry, sandy sites. Look for it before the orchard is planted because it can’t be controlled afterwards, Smith said. A ten-lined June beetle larva is easy to see in the ground. It is white with a red head and is about the size of a little finger.
"If you find them, you have to fumigate with a product that’s insecticidal, like Telone [1,3-dichloropropene]," he added. "The only thing that’s worked so far, relatively consistently, has been fumigation."
Fumigation also helps counter replant disease, which is likely to be a problem when any type of tree fruit is planted after tree fruits. Even grapes planted after tree fruits have been affected, Smith reported.
"Fumigation with the right product, done properly, is almost one of those miraculous things. If you can’t fumigate a replant site, don’t plant!"
Replant disease is caused by many different living organisms, and the combination of organisms probably differs from one site to another. Fungi are probably involved.
In trials, Smith has demonstrated a huge difference in growth of trees on fumigated and unfumigated ground. Sick trees don’t grow as well and produce smaller fruit.
In a trial in a Gala orchard at Orondo, Washington, gross returns were $67,000 per acre higher in the fumigated plots over the 17-year life of the orchard, he reported.
"That’s the difference in value fumigation gives you," he said. "That’s why I almost jump out of my shoes when people say, ‘I didn’t fumigate because it costs too much.’ Fumigation costs you $500 to $700 per acre. You’re gambling $65,000. Those are pretty bad odds."
Fumigation pays back in the first crop, he has found. He calculates that the fumigation that’s been done over the past 25 years in Washington State has boosted grower returns by a total of $1.4 billion, yet not all orchards are fumigated. In fact, only about 60 percent of new plantings are fumigated.
Fumigation is best done in the fall, and it needs to be done properly because uneven fumigation can lead to uneven tree growth, Smith said. Uneven growth can be a problem in new orchard systems.
Smith recommends Telone C17, which includes chloropicrin. It can be applied at 30 gallons per acre in eight-foot-wide bands. However, if the between-row spacing is narrow, it might as well be broadcast over the entire site. Telone C35 contains more chloropicrin, but Smith said the two products seem to perform about the same.
Vapam (metam sodium) is difficult to apply properly, though if it is done correctly, it can be as good as Telone. He recommends hiring a commercial applicator.
If growers miss the opportunity to fumigate in the fall, they can do it in the spring as soon as the ground is workable and wait a month before planting the trees. Smith said it’s better to delay planting than skip the fumigation. "Even if you plant in June, you would be better off than not fumigating. You cannot make up for not fumigating—ever."
Smith was asked if a site needed to be fumigated if it was previously planted with alfalfa.
"I think planting after alfalfa is a sure-fire way to get tree growth, and I have never recommended fumigating except following another tree or woody plant," he responded. "We’re worried about pathogens that are specific to the roots of perennial plants, especially those in the rosaceous group."
However, if there are still root suckers in the ground from a previously removed orchard, the pathogens will still be there, and fumigation will be necessary, he said.