Weed And Disease Control In Organic Apple Orchards

Weed Control
Plans for weed control should be in place prior to planting the orchard. Many options have been investigated, and the perfect option remains elusive. Hay mulches and synthetic mulches harbor vole populations, and controlling weeds along edges of synthetic mulches is difficult because mowers snag the mulches. Some burn-down herbicides are approved for use in organic plantings, but these are expensive and must be reapplied frequently. Propane flamers sound like fun for pyromaniacs but are expensive and have proven only marginally effective over the long haul.

Wood chip mulch has provided acceptable weed control without harboring voles, but the transport and installation costs for a wood chip mulch can be substantial. Wood chip mulches must be renewed every several years, and perennial weeds such as Canada thistle can become a problem in wood chip mulches. Wood chip mulches provide some benefits for fertility and moisture retention, but long-term management is more complex than for weed control by tilling. Wood chips should never be tilled into the soil because they will tie up all of the available nitrogen for several years after incorporation. Thus, one cannot mix wood chips and tillage.

An option worth exploring would be a removable and re-usable synthetic mulch. Several companies manufacture durable plastic and/or fiberglass-based ground covers that have worked well to suppress weeds. When left in place during winter, these mulches harbor damaging populations of voles. However, it should be feasible to design a machine that would mechanically install the mulch in spring (perhaps in early May) and then recover that mulch onto a roll in mid-August so that it could be stored until it is reinstalled the next spring. A plastic mulch installer like those used for vegetables might be modified and off-set so that a ground cover could be installed on one side of a tree with the outside edge buried in soil to hold it in place. After installation was completed on both sides of a tree row (with separate 3-foot-wide strips of mulch on each side), the center overlap along the tree row would need to be manually stabilized to resist wind by inserting long wire “staples” into the ground or by weighting the center edge with rocks, wood chip mulch, or a long water-filled hose. Wood chip mulch installed over removable synthetic mulch could presumably be shaken to the ground when the synthetic mulch is removed in fall and then covered over with the synthetic mulch the next year. However, removable synthetic mulches need to be tested experimentally and will become practical only if their installation and removal can be mechanized.

Disease Control
Various plant pathologists working with organic apple production have all agreed that the two most problematic groups of diseases in organic apple production are rust diseases and summer fruit rots. Sulfur and liquid lime-sulfur (LLS) can be used to control most other diseases, although, as noted before, using these fungicides at the rates and intervals needed to control apple scab will cause yield reductions. To date, all of the organic fungicides promoted as alternatives to sulfur are more expensive and less effective than sulfur.

Fire blight is another potential problem with many cultivars, but streptomycin is currently acceptable within organic programs so long at is used only on an as-needed basis. Strategies for fire blight control are therefore similar in organic and conventional orchards.

Cedar apple rust and quince rust are very difficult to control with sulfur. Therefore, organic plantings that include rust-susceptible cultivars should be located at least 300 feet away from the nearest cedar trees. Powdery mildew can become a problem on some cultivars, but three or four applications of sulfur beginning at petal fall may suffice to keep mildew in check. Where mildew becomes established, however, the sulfur program should be initiated no later than pink.

Sooty blotch and flyspeck can be controlled by using low rates of LLS during summer. In trials in New York’s Hudson Valley, LLS applied at 1 quart per 100 gallons of dilute spray was very effective when applied on a 10-day schedule during July and August, whereas 2 quarts per 100 gallons were required for good control on a 20-day schedule. In regions where conditions favor development of flyspeck and sooty blotch, sprays with LLS must be continued into late September to prevent disease on late-maturing cultivars.

Unfortunately, LLS does not control summer fruit rots such as black rot, white rot, and bitter rot. Low rates of copper fungicide can be tank-mixed with LLS during late July and August LLS to increase activity of these sprays against summer fruit rots. However, organic apple growers may need to resort to sanitation measures to control summer fruit decays as plantings mature. In the northeast, much of the inoculum for summer fruit decays comes from fruitlet mummies that are retained after fruit set and that remain on the trees over winter. Manually removing all of these fruitlet mummies during winter pruning should significantly reduce problems with summer fruit rots. However, as is the case with many other aspects of organic production, that hypothesis has not yet been tested.

Leave a Reply

Featured Stories

CEU SeriesCEU Series: Pesticide Labels Are A Must-Read
November 1, 2014
Be cued into what's on the container as well as safety data sheets. Read More
CitrusForecast: South Florida Dry Season May See Fair Share Of Damp Days
October 31, 2014
Outlook calls for possible above-normal precipitation around region for fall and winter months. Read More
ProductionDrought Forcing California Growers To Rely On Groundwater
October 31, 2014
While the state issues curtailments to those with junior rights, growers are increasingly relying on groundwater to irrigate their crop. Read More
Crop ProtectionThe Unlikely Parallel Between Human And Plant Health
October 31, 2014
One of the notable national developments in the summer of 2014 was the unexpected occurrence of serious respiratory infections in Read More
VegetablesWhy You Should Be Trialing New Vegetable Varieties
October 31, 2014
Selecting high-performing selections is no easy task. Read More
FruitsCalifornia Growers Sue State Over Drought
October 30, 2014
They claim the State Water Resources Control Board illegally denied water deliveries. Read More
CucurbitsNew Watermelon Planting Program For The Southeast U.S.
October 30, 2014
Sakata seeking to make regional impact by providing in-demand material through several local producers. Read More
Leafy Vegetables3 Can’t-Miss Cabbage Varieties For Florida Growers
October 30, 2014
Reed's Seeds highlights a trio of high-performance selections for Sunshine State producers. Read More
Insect ControlTake Control Of Thrips In Your Greenhouse
October 30, 2014
Why such a foreboding title? Thrips, one of the tiniest pests of greenhouse crops, are the carrier of one of Read More
BerriesManage Black Root Rot Of Strawberry
October 30, 2014
Controls include preplant nematode analysis, three-to-five year crop rotations, and more. Read More

The Latest

CEU SeriesCEU Series: Pesticide Labels Are A Must-Read
November 1, 2014
Be cued into what's on the container as well as safety data sheets. Read More
CitrusForecast: South Florida Dry Season May See Fair Share O…
October 31, 2014
Outlook calls for possible above-normal precipitation around region for fall and winter months. Read More
ProductionDrought Forcing California Growers To Rely On Groundwat…
October 31, 2014
While the state issues curtailments to those with junior rights, growers are increasingly relying on groundwater to irrigate their crop. Read More
Crop ProtectionThe Unlikely Parallel Between Human And Plant Health
October 31, 2014
One of the notable national developments in the summer of 2014 was the unexpected occurrence of serious respiratory infections in Read More
VegetablesWhy You Should Be Trialing New Vegetable Varieties
October 31, 2014
Selecting high-performing selections is no easy task. Read More
FruitsCalifornia Growers Sue State Over Drought
October 30, 2014
They claim the State Water Resources Control Board illegally denied water deliveries. Read More
CucurbitsNew Watermelon Planting Program For The Southeast U.S.
October 30, 2014
Sakata seeking to make regional impact by providing in-demand material through several local producers. Read More
Leafy Vegetables3 Can’t-Miss Cabbage Varieties For Florida Grower…
October 30, 2014
Reed's Seeds highlights a trio of high-performance selections for Sunshine State producers. Read More
Insect ControlTake Control Of Thrips In Your Greenhouse
October 30, 2014
Why such a foreboding title? Thrips, one of the tiniest pests of greenhouse crops, are the carrier of one of Read More
BerriesManage Black Root Rot Of Strawberry
October 30, 2014
Controls include preplant nematode analysis, three-to-five year crop rotations, and more. Read More
FruitsSexual Evolution May Bear More Fruit In The Orchard
October 30, 2014
Scientists take a closer look at genes and find new plant breeding possibilities. Read More
Apples & PearsWashington Apples To Restart Shipments To China
October 29, 2014
Agreement reached between U.S. and Chinese governments to reinstate market access after two-year absence. Read More
EquipmentEnter To Win A Kubota At The Washington State Horticult…
October 29, 2014
Attendees have a chance to take home a new utility vehicle courtesy of Wilbur-Ellis and Western Fruit Grower. Read More
CitrusUSDA To Provide $4 Million For Honey Bee Habitat
October 29, 2014
The funds will go toward helping growers implement conservation practices to improve honey bee health. Read More
FruitsHuge California Drought Meeting Planned
October 29, 2014
State, federal officials to meet as forecasts for the coming year look bleak. Read More
PotatoesNew CEO At Black Gold Farms, A Top 100 Grower
October 28, 2014
Eric Halverson takes the reins at the potato operation, while his father Gregg will remain president of the farm’s board of directors. Read More
FruitsValent U.S.A., MGK Enter Into Marketing Agreement
October 28, 2014
Valent U.S.A. to manage the marketing and sales of MGK’s crop protection line of insect control products beginning in April 2015. Read More
VegetablesMultistate Land-Grant University Research Project Contr…
October 28, 2014
The project began in the 1970s as a Regional Initiative and has since expanded Internationally. Read More