Mark Longstroth

Summary: Southwest Michigan apple orchards suffered severe fireblight damage in 2000. Fire blight is a highly contagious disease of apples and pears caused by a plant-eating bacterium. The epidemic followed unusually warm, humid, and wet weather during bloom in May. Heavy rains, often with hail, dispersed the disease throughout the apple growing region intensified the threat to the area's apple-growing industry. This fireblight epidemic destroyed hundreds of acres of high-density apple orchards with the death of most of the trees. Over 250,000 apple trees were killed and over 1,000 acres of appleess were lost.

The development cost of these orchards was over $ 9 million. Apple yields will be reduced by 35% over the region. Some growers will suffer 100% losses in some plantings. The Southwest region produces an average of 4.5 to 7 million bushels and the expected crop loss is 2.7 million bushels about $ 10 million. It will take at least 5 years for yields to recover with a cumulative loss of yield of nearly $ 36 million. The region's total economic loss is almost $ 42 million.

The apple industry in Southwest Michigan will likely never be the same. The perfect blight conditions of 2000 occurred previously in 1991 when the industry was less vulnerable. It will be very difficult for apple growers to learn to manage fireblight given the current lack of premium fireblight resistant varieties. In addition, strains of the fireblight bacterium resistant to streptomycin are widespread in Van Buren County and were detected in orchards in neighboring Berrien County this year. Streptomycin has been the single bullet for fireblight control and it will be several years before chemicals in the registration pipeline will be available to replace it. Orchards can get through average blight years with existing controls, only to sustain devastating losses in 5 to 10 years when perfect fireblight conditions occur.

Improving current blight susceptible varieties through genetic engineering shows considerable promise for the future, but the public's negative view of genetically altered crops will need to be overcome before orchardists can utilize this new technology. The new blight-resistant rootstocks from conventional breeding will help growers most years, but only resistant varieties combined with resistant rootstocks will allow growers to avoid losses in perfect blight-favorable years such as 2000.

Antibiotic sprays applied during bloom are used to control fireblight. A computer program called MaryBlyt is used to track disease development and time antibiotic applications. Streptomycin, the most commonly used antibiotic for fireblight control, gives good control if used immediate before infection or within about 12 hours (24 hours maximum) after an infection. Oxytetracycline is used to control fireblight where streptomycin resistance exists. Oxytetracycline must be applied before an infection to be effective.

A mix of fresh market and processing apple varieties are grown in Southwest Michigan. Key apple varieties such as Gala, Idared, Jonathan, and Jonagold are very susceptible to fireblight; Golden Delicious and Romes are less susceptible; and a few such as Red Delicious are almost resistant. In order to preserve the economic viability of the Southwest Michigan apple industry, many new plantings of these varieties were established in the region during the last decade.

Apples are grown on rootstocks that increase the size and quality of the fruit and overall fruitfulness of the trees. Common dwarfing rootstocks such as Malling 26 (M26) and Malling 9 (M9) are very blight susceptible; they may even increase the susceptibility of the scion varieties. Rootstocks can become infected by direct infection of rootstock suckers at the base of the tree or when bacteria travel symptomlessly through the trunk into the roots. Infected rootstocks are quickly girdled killing the tree. Such systemic movement from a minor infection can result in tree death, even of resistant Red Delicious trees.

The Size and Structure of the Southwest Michigan Apple Industry

This fireblight epidemic in Southwest Michigan affects primarily Berrien and Van Buren counties, the two largest fruit growing counties in the region. But other counties such as Allegan, Branch, Cass, Hillsdale and Kalamazoo and St. Joseph also have severely affected apple plantings. Today, in 2000, there are probably 6000 acres of apples in both Berrien and Van Buren Counties, 1300 in Allegan, and 2000 in the rest of the affected counties.

Southwest Michigan apple growers have suffered from poor prices for the last several years and many older growers have reduced inputs into their apple orchards by reducing pruning and fertilizing. The resulting trees have less new growth and are unlikely to suffer greatly from fireblight infection. While these trees are still vulnerable to infection it is less likely to cause tree death or dramatic yield losses. With reduced maintenance, yields and fruit quality on these trees declines. Growers who can not afford to maintain their orchards will not do the dormant pruning necessary to remove overwintering cankers that serve as the primary inoculum in the spring for fireblight. Reducing inputs is not a viable long-term strategy and these orchards soon fail.

The next step after reducing inputs is orchard abandonment. There are probably over a thousand acres of abandoned orchards in Berrien and Van Buren counties. These orchards have been abandoned or sold by their owners. In many cases the new owners are not fruit growers, but urban emigrants who desire rural land. They are unable to maintain the orchards and unwilling to remove the trees because of the high cost of removing fully grown standard apple trees 30 to 50 years old. These orchards serve as a reservoir for fireblight as well as other pests and diseases of apples and increase the costs and difficulty of maintain adequate disease management programs in neighboring orchards.

During the last decade, progressive Southwest Michigan apple growers have shifted from conventional plantings with 55 to 499 trees per acre to high density plantings with more than 500 trees/acre. These new high value plantings utilized increasingly popular M26, M9 and Mark rootstocks. There were approximately 1,500 acres of fireblight susceptible dwarfing rootstocks in Southwest Michigan in 1997 and new plantings on these rootstocks were being added at 100 or more acres per year. In 2000, there was a total of about 2000 acres of high-density plantings. There are 500 to 700 acres, which are 5 years old or less, which could be killed outright by fireblight. In addition, many older high density planting involving highly susceptible varieties will also be lost.

Apple planting in Southwest Michigan averages about 400 acres per year so that 2000 acres would be five years old or less. Most apples planted in recent years have been newer varieties such as Gala, Fuji, Braeburn etc. These varieties receive a premium price for fresh market fruit. The economics of the apple industry in the last several years have reduced profit margins to the point that large older trees are not profitable to maintain. To preserve the economic viability of their orchards, many of the top growers in the region have been busy replacing older plantings of standard and semi-dwarf trees with high-density orchards using dwarfing rootstocks. Yields of high quality fresh market fruit from these plantings quickly climbs to high levels that should be sustainable.

The remainder of the apple production in Southwest Michigan is processed into sauce, slices, and juice by area processors. Jonathan is preferred among all other varieties for the manufacture of frozen slices and Idared and Rome are preferred variety to manufacture apple pie slices and for use in applesauce. These varieties are susceptible to fire blight injury and subsequent tree death. In 2000, large blocks of these varieties suffered with severe fire blight.

Streptomycin-resistant fire blight was found in Van Buren County in 1990 and resistance had spread countywide by 1999. A few growers use a costly but relatively effective combination of streptomycin plus oxytetracycline, and these growers are more active in following MaryBlyt predictions in an attempt to apply treatments just ahead of an infection. Most other growers use less costly and weaker treatments of oxytetracycline, copper, or Aliette, or continue to use streptomycin despite resistance, or do not treat with any chemical. Where possible, treatments are applied before infection periods are predicted by MaryBlyt, but in practice are more likely to be applied after an infection. A few Van Buren County growers have avoided new plantings of fireblight susceptible varieties and susceptible dwarfing rootstocks. However, they have older fireblight susceptible plantings and are concerned about what varieties to plant in the future.

Many acres of high-density apple plantings have been severely affected by this epidemic. These orchards will be destroyed as economic units by the death of most of the orchard's trees. This epidemic will change the way we grow apples in Southwest Michigan. Few growers will again chance the risk of planting the new premium varieties hoping to maintain profits in a market with global oversupply, believing they could control fireblight. A major unanswered question is what varieties can be grown profitably in the future without undue fire blight risk.

The 2000 Fireblight Epidemic

Because of the warm growing conditions in the spring fireblight is a perennial disease problem in Southwest Michigan. Growers typically apply 2 to 3 sprays of antibiotics during bloom and save the final spray for use after a hailstorm or other trauma. In Southwest Michigan the question is not will you have fireblight it is how bad will it be?

In 2000, fireblight symptoms began to appear in some Idared and Jonathan orchards several days earlier than predicted by the MaryBlyt model. Backtracking from the date of the symptoms indicates that the initial infections took place on May 7 and 8 when predicted bacteria levels reached record high levels. There was no rain or prolonged dew on these dates, but the average daily relative humidity values were 79.2% and 80.5%, respectively. Although rare in occurrence, infection can occur during dry periods when daily relative humidity values are above 70%. With minimum nighttime temperatures of 65 and 68 F, respectively, bacterial populations increased throughout each 24-hour period resulting in very high populations; populations that overwhelmed subsequent antibiotic treatments. Orchardists who applied antibiotics ahead of this weather achieved the best control. Beginning May 9, MaryBlyt subsequently predicted three infection periods associated with rain and favorable temperatures. Golden Delicious and Rome were in bloom and bloom blight was common on these varieties while all varieties suffered trauma blight from the heavy storms.

As the symptoms of the blossom and trauma infections began to appear, a cold front with wide spread hail and thunderstorms moved through the region on May 18. The blossom blight symptoms that began to appear in mid May appeared mainly in unsprayed blocks of susceptible varieties, and also in varieties such as Golden Delicious that do not normally get fireblight and were not sprayed. Fireblight strikes could also be found on varieties that are normally very resistant such as Empire, McIntosh and Red Delicious. This indicates we had extremely high levels of inoculum and good infection conditions. But the rainstorm on May 18 spread the disease though out the growing region. This large-scale weather event lasted for several days. It spread the disease to many previously uninfected blocks. Growers who applied antibiotics after rains were hard pressed to cover all their acreage within 24 hours. In addition this weather system spread the fireblight strains that are resistant to streptomycin to a large area where they previously where not found. It seems that were streptomycin resistant fireblight is found the use of streptomycin makes the disease worse because it removes competitors of the bacteria, which normally slow its spread. This means that the application of streptomycin actually increased the severity of the disease in some orchards.

This Jonathan orchard was found to contain streptomycin resistant fireblight.

At the beginning of June, another wave of fireblight symptoms began to appear in all susceptible varieties as a result of the trauma for wind heavy rain and hail. The symptoms from this infection are very severe and widespread. Most apple growers who planted new trees in the last five years will lose those plants. Others are concerned about the health of their older orchards. And all apple growers will lose a portion of their crop for the next several years.

Loss Estimates

The Southwest Michigan apple industry will be severely affected for at least the next 5 years. Large portions of this year's crop have been lost due to the death of the branches and trees that supported the fruit. Many young orchards will need to be replanted; about 5 years will be required for these orchards to return to significant production. In mature orchards, 3 to 5 years will be required to grow new branches and restore production.

These Golden Delicious trees will probably survive, but they will lose most of this year's crop.

The Southwest Michigan apple crop varies from 4.5 to7 million bushels with a gross grower income of $ 30 to $ 40 million each year. Yield losses will probably be in the 20% to 70% range for most apple varieties. Some individual grower losses will be much higher. The total expected production loss for the region in 2000 is estimated at 2.7 million bushels, 113 million pounds. Using 9 cents as an average price per pound the total crop loss is $10 million. 2.7 million bushels or 113 million lb. at an average price of $.09/lbs. equals $10,179,000 loss. About 2/3 of the region's apple crop is processed and processing prices ranged from 4.5 to 9.5 cents/lb. in 1999. Fresh Market returns vary from 17 to 4 cents per lb. Returns depend on variety and grade and percent pack out.

The 2000 apple crop was expected to be off from previous years due to a heavy crop in 1999 and a severe frost in early April that probably reduced the 2000 apple crop by 20% or more. The part of the apple tree that was killed will not bear a crop next year. Apples bear their fruit on 2 year-old wood, so yields will not rise greatly until 3 years from now. If the tree is not killed it will probably be back to full production in 5 years. Losses in 2001 would be almost equal to 2000, then yield should begin to rise. For older trees (7 years or more) this increase in yield should end in about 5 years.

If the initial loss is about one million bushels the cumulative loss over 5 years will be about $ 15 million. For an initial loss of 2.5 million bushels then the loss will be $ 32 million. An average loss figure for the region would be $ 25.5 million.

Estimated Tree and Acreage Losses for 2000

These young trees will certainly die

Young trees are very vulnerable to fireblight. I anticipate that most susceptible young trees from one to 5-years old will be killed in this epidemic. Trees from 5 to 7 years old will be severely damaged and many will die. Orchards that lose more than 20% of their trees are no longer economically viable and the orchard will need to be replaced. I do not believe that replanting into an existing orchard is economically viable once the orchard is more than 5 years old and the entire orchard or sections of the orchard should be removed. The extra cost of maintaining small trees in an older planting until they reach full size is not generally worthwhile.

I estimate the loss at 1550 acres, a lost investment of $9,300,000. I estimate that growers will lose; 720 acres of 1 to 3-year old trees; 240 acres of 4-year old trees; 251 acres of 5-year old trees, 165 acres of 6-year old trees, 120 acres of 7-year old trees and 46 acres of 8-year old trees.

Bill Shane has estimated the loss of 2,300 acres, a lost investment of $8,800,000. Bill estimates that growers will lose 500 acres of 1-year old trees; 800 acres of 2-year old trees; 375 acres of 3-year old trees; 200 acres of 4-year old trees; and 75 acres of 5-year old trees. Apple trees 6 years and older are estimated at a loss of 360 acres.

County Loss Estimates

Advice for Growers

My advice to growers with severe fireblight at this time is to do nothing. Most of the damage for the year has already been done. There is no spray or cure for fireblight once it is in the trees. If there are only a few strikes in the orchard then pulling out shoots makes sense when symptoms first appear. But when there are many strikes in each tree then waiting until the disease stops spreading is a good option. Many Southwest growers have abandoned their crop in severely affected young orchards and sprayed with copper hoping to slow the spread of the disease. This is little more than a feel good option. It only reduces the population of bacteria on the trees. Copper has no effect on the bacteria in the trees. If your trees need calcium or potassium now is a time to apply it.  These calcium helps maintain cell walls and membranes. Potassium is very important in water relations and may slow the advance of the disease in older tissues. I am not suggesting that you spray these materials on to trees.  It would be more effective to determine what your orchard needs are and apply them at the usual time.

My recommendation is that fireblight affected branches be pruned out this winter. Several trips through the orchard should be made to be sure that all fireblight-affected branches are removed. Many growers in Southwest Michigan apply copper in the early spring. Next year I recommend we all do it.