Tree Fruit Leader, Vol. 4(2) Dec. 1995

About Weeds, Spartan, Fuji, Deep Ripping and Density

by Mike Sanders, P.Ag., Tree Fruit Specialist, BCMAFF, Kelowna

How effective is your weed program? 

It is well recognized that good weed control is mandatory if optimal growth and yields of young plantings are to be obtained. What is not recognized, however, is the degree of weed control required. 

Research from Cornell University in New York has shown that growth restrictions of over 40% have been measured in apple trees during the planting year from only moderate annual weed competition. Similar studies from Cornell showed that a single month of weed suppression early in the growing season (April/May) is more beneficial than three months of suppression later in the season. Also, the effects of this early weed control showed up in growth and yields for the first three years in the orchard. 

To explore weed effects in young plantings in more detail I talked to Dr. Eugene Hogue at the Summerland Research Station. Eugene has worked with chemical and non-chemical weed control and has studied the impact of weeds on tree growth. 

Eugene believes that newly planted apple trees on dwarfing rootstocks are very sensitive to competition from weeds. Weed levels tolerated by older trees cannot be tolerated by young trees. *

Apparently a good stand of even small weeds in the vicinity of trees can affect tree growth. This is because trees have limited capacity to compete because of restricted root systems. Data collected in several of his trials have shown that trees in hand weeded plots, that is, whenever weed growth reached 2-3 inches, had less growth at the end of the season than trees in some of his herbicide treated plots. Generally this improved growth was found in plots receiving low rates of a combination of residual herbicides. The combination of chemical allows you to control a broader spectrum of weeds and the low rates gives you the added protection against toxicity to the shallow rooted trees, especially in coarse soils. 

Eugene feels that weeds can provide harmful effects on young trees that go beyond competition for nutrients and soil moisture. In other plots where all the necessary water and nutrients for both trees and weeds left to grow in the vicinity of the trees were provided, even the luxury levels could not prevent a growth retarding effect.

 . . . . weeds emit "something" that stifles tree growth. 

Why is this? Eugenes' feeling is that some weeds emit "something" that stifles tree growth. He has not tested this concept with all weeds, but has shown very positively that this is the case with quack grass. 

My analysis of this information is that for optimal growth and yields of young plantings most growers are going to have to improve their weed control program and start much earlier in the season. If non-residual materials are to be used (paraquat, glyphosate) more frequent applications will be necessary, even though weed mass might seem low. The better bet may be residual materials or mulches. Initial costs may be higher in some cases but weed control will improve as will tree growth, yields and profits.

Blind Wood On Spartan 

Many growers have commented on the blind wood problem on Spartan branches. In some cases 50% of branches are bare reducing yield potential. This is a genetic problem related to growth habit. 

Heading cuts in the dormant season reduce the problem but are not acceptable as the result is only several strong branches in the vicinity of the cut. I have found delayed heading to be far more satisfactory than dormant heading. This is usually done around the middle of May when new growth is about 6 inches long. The tuft of new growth is removed just below the lowest leaf. Following this delayed heading the tree can almost be leafless for 10 days or so but then the tree fills in with new shoots. This treatment is often necessary for two or three years. Other tip bearing varieties such as Rome and Tydeman also respond well to this treatment.

Biennial Fuji 

The biennial bearing nature of Fuji was clearly evident this past growing season. Far too many blocks that carried good crops in 1994 came back with light crops in 1995. 

Fuji sets well and at the same time is a difficult cultivar to thin. This is a big factor in biennial bearing. Part of the reason for difficulty in thinning may be the extended blossom season making timing of any blossom materials difficult. More than one application will probably be necessary in some years. 

In the last two growing seasons I have done chemical thinning trials with Fuji. In 1994 ATS was tested at different rates. Some thinning occurred but the degree of thinning was not earth shattering and the amount of return bloom was not very good. At the highest rate tested (2.0 L/100L) some leaf injury occurred. 

Because of the relatively disappointing results from 1994, a more aggressive approach was taken in 1995. Twenty different treatments and combinations were tested in 2 plots. The greatest amount of thinning resulted from 2 ATS applications followed by NAA plus Sevin. This treatment caused slight over-thinning. From these plots it seems that ATS might become an integral part of a Fuji thinning program probably followed by Sevin or even Sevin plus NAA. More fine-tuning, however, is required but growers should be trying different materials and combinations. 

Ethrel at 200 ppm was tested by itself or with other materials. Results of this were not significantly better than untreated trees. Ethrel has been tried as a Fuji thinner in other fruit growing areas with varying degrees of success. The problem with Ethrel is that it has caused some russet problems in other areas although damage was not observed in local plots. Return bloom results from these 1995 plots cannot be determined until next spring. 

Fuji is susceptible to russet so care must be taken with all spray materials, especially near the blossom period. This is one reason why caution should be exercised with petal fall applications of Sevin. 

Norm Looney of Summerland Research Station also did some fruit thinning work with Fuji in 1995. He has some pretty interesting results with Accel and Sevin. Accel is a new growth regulator that is not yet registered in Canada. 

The biennial bearing problem with Fuji may be a bigger problem than most people think and chemicals may not be the only solution. A combination of chemical materials and cultural treatments may very well be necessary.

A hint that cultural techniques might help overcome biennial production comes from research by Yoshio, Fan and Patterson. In Fruit Varieties Journal they reported that early fruit thinning to 1 fruit per 5 terminal buds and 75 leaves per fruit resulted in adequate return bloom and good fruit size. Some of this early fruit removal could be accomplished with selective dormant pruning. 

The type of fruiting wood to remove will no doubt be important. When in Japan last March, I visited a very progressive and knowledgeable grower who has been able to keep Fuji bearing annually. He believes that the best Fuji fruit is produced on fruiting wood that ranges from 3/4" to 6" long. He regularly removes all fruiting wood that does not meet this requirement during the dormant period. By following this pruning program and applying Sevin once each season he has been very successful at keeping trees bearing annually. This coincides with the above information. It's worth trying!

Variety Testing 

At the Horticultural Forum PICO managed a taste testing of a number of apple cultivars. The winners in order of preference were 8M 15-10, Ambrosia and Jonagold and 8B 14-56 (tie for third). My own taste buds agreed with the first and second place finishers and I have always liked Jonagold. 

Of course, we have all learned that a new variety cannot be selected on taste alone. Much more information is necessary.

From my point of view, one of the other important facts is how crispy and crunchy are these selections out of storage and on the shelf? PICO has been doing a commendable job of evaluating many new selections and can provide you with considerable horticultural and marketing information.

Digging Deep 

Several comments have been made this fall about excellent tree growth responses in sites that were subsoiled (chiseled, deep ripped) prior to planting. This has been a recommended practice for a number of years but most growers overlook subsoiling in their preparation for new plantings. 

Subsoiling increases depth of non-compacted soil. This facilitates deeper root and water penetration as well as increased water and nutrient availability. Subsoiling may prove detrimental on sites where salts are brought to the surface. 

For information on subsoiling refer to Soil Management Handbook for the Okanagan and Similkameen Valleys available from BCMAFF offices.

The Density Challenge 

The trend of apple replanting over the past several years has been to higher and higher densities. A few growers have even planted more than 5,000 trees per acre. This planting trend has been pushed along by the enthusiasm of super spindle technology and perhaps even competitive spirit that says "I can plant more than you". 

Is there an economic upper limit of density whereupon further investment in trees starts to show declining returns? 

The Economic Law of Diminishing Returns provides a key to assessing this point in decline of added returns. This law, very loosely stated says: "if the level of inputs to any fixed supply of land are increased, the crops obtained from the land will rise, but sooner or later output will increase at a slower rate than the rate at which inputs are added". 

To determine the density level at which returns begin to decline, George Geldart ran analyses of 10 different densities ranging from 400 to 3,500 trees per acre. The main assumptions were: yield at maturity of 35,000 pounds per acre; returns of 35 cents per pound and a time period of 10 years. 

The results of the analysis showed that peak potential profitability occurred at somewhere between 1,000 and 1,400 trees per acre (11' x 4' to 10' x 3'). These results are interesting as they are fairly similar to the results found in Tyrolia indicating the most profitable plantings under their conditions to be in the range of 1,200 to 2,000 trees per acre. 

The downside with these densities is that we don't know how long plantings of these densities can maintain production of good yields of high quality fruit. There just hasn't been enough experience under our conditions and market requirements to determine this. My guess under good management is a maximum of from 8 to 12 years for densities in the range of 1,000 to 1,400 trees per acre. 

The advantage of such densities is that they are easy to manage. Except for the lower of these densities, trees will not be headed at planting and the main effort through the years will be to remove strong growth, calm the top and shorten back fruiting wood. Pruning unheaded trees is much faster than with headed trees and most of the work is done during the summer. In effect, the tree at maturity will be a narrow vertical axis and this type of tree has always been easy to manage. 

I do not view these densities and the training system as the ultimate in orchard design. We are in a business that is constantly evolving. Over time, as more is learned, orchard design will be based on variety characteristics, fruit quality, labor efficiency and the economics of the day (interest and inflation rates). In the short term, however, the densities referred to appear to be the best way of maximizing potential returns provided you have necessary management skills. If you don't think you have the experience to manage such plantings, it may be appropriate for you to consider vertical axis or slender spindle training at densities of 650 to 850 trees per acre.

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