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 fi^^\\ United States 
 Department of 
 Agriculture 
 
 Combined Forest Pest 
 Research and 
 Program Development 
 
 Home and Garden Bulletin 
 
 No. 223 
 
 UNIV. OF FL LH. 
 DOCUyEfJTaDEPl 
 
 L 
 
 U.S. DEPOWTOHY 
 
 Gypsy Moth 
 Handbook 
 
 Defoliation 
 by the 
 
 Gypsy Moth: 
 How it Hurts 
 Your Tree 
 
 Z:^ }}:^i047^ 
 
 is' 
 
 |5 JAN 
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 19T8 ^^ 
 .• * / 
 
Defoliation by the Gypsy 
 
 Moth: 
 
 How it Hurts Your Tree 
 
 by 
 
 Philip M. Wargo' 
 
 In 1974 the U.S. Department of 
 Agriculture initiated the 
 Combined Forest Pest Research 
 and Development Program, an 
 interagency effort that 
 concentrated on the Douglas-fir 
 tussock moth in the West, on the 
 southern pine beetle in the South, 
 and on the gypsy moth in the 
 Northeast. The work reported in 
 this publication was funded in 
 whole or in part by the program. 
 This manual is one in a series on 
 the gypsy moth. 
 
 Leaves are a pleasant background 
 for our houses and provide relief 
 from a hot sun. They also act as air 
 filters by removing dust and 
 pollutants from the atmosphere, 
 and buffer our ears from the noises 
 generated by our daily activities. 
 Leaves also provide beauty and 
 color throughout the year. The 
 main purpose of leaves, however, 
 is to produce food for the tree so it 
 can produce wood and more leaves 
 for the next year. 
 
 Defoliation caused by hungry gypsy 
 moth caterpillars (larvae) eating the 
 leaves may deprive us of a tree"s 
 beauty and benefits temporarily for 
 1 or several years (figs. 1 and 2). 
 But we might be left permanently 
 without these benefits, because 
 defoliation can result in dead, 
 leafless trees (fig. 3). 
 
 Figure 1. — Ragged foliage that 
 has been chewed by the gypsy 
 moth caterpillar. 
 
 ' Research plant pathologist. Forest Insect 
 & Disease Research 1 .ahorator\ . Hamden. 
 Conn. 
 
When an oak tree (the primary food to use its food reserves. This can 
 
 source of the gypsy moth) loses its 
 leaves for any reason other than 
 the onset of winter, its natural 
 growth and food-making cycles are 
 interrupted. The tree may not 
 produce enough food and may have 
 
 weaken the tree, leaving it 
 vulnerable to attack by insects and 
 fungi. 
 
 Figure 2. — Closeup of the gypsy 
 moth caterpillar in its later 
 growth stages when it is fairly 
 large. 
 

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 Whether a tree ends up as a cutoff 
 stump or a functional living tree 
 after defoliation depends on how 
 badly the tree was affected by 
 defoliation, and this depends on: 
 
 • How much foliage was eaten 
 
 • If the tree refoliated 
 
 • How many years in succession 
 the tree was defoliated 
 
 • When during the year defoliation 
 occurred 
 
 • What the weather conditions 
 were after defoliation 
 
 • If disease organisms and other 
 insects attacked the tree 
 
 • How healthy or vigorous the tree 
 was before defoliation. 
 
 These criteria are discussed in this 
 booklet. When you finish reading, 
 you should understand why 
 defoliation hurts your tree and have 
 some idea about your tree's 
 chances for survival if it has been 
 defoliated by the gypsy moth. 
 While this booklet does emphasize 
 defoliation of oak trees by the 
 gypsy moth, the information applies 
 to defoliation of other deciduous 
 trees (a tree that sheds its leaves 
 each autumn) and to other insects. 
 
 Figure 3. — Oak trees that have 
 died after heavy gypsv moth 
 defoliation. Oaks in foreground 
 have been cut dovsn for tlreuood. 
 
1. How much foliage was eaten? 
 
 4A 
 
 One of the most important factors 
 is how much foliage was eaten by 
 the gypsy moth caterpillar. The 
 more foliage the insect eats, the 
 less food is produced for the tree 
 (fig. 4). 
 
 The worst situation for the tree is 
 when all the foliage has been eaten. 
 With all the leaves gone, the tree 
 has no food-producing system, and 
 it must live off its reserve foods 
 until the new leaves appear. These 
 reserve foods are used normally to 
 feed the tree during the winter 
 
 resting period. If the tree enters 
 winter with low food reserves, 
 some parts of the tree may die. 
 
 Apparently a tree can lose up to 
 half its foliage before it begins to 
 suffer. When more than half the 
 foliage is eaten, the tree begins to 
 change because not enough food 
 and other growth substances are 
 being produced. 
 
 Figure 4. — Oak trees in various 
 stages of defoliation: A, No 
 defoliation; B. light defoliation; 
 C. moderate defoliation; D. 
 heavy defoliation. 
 
2. Did the tree refoliate? 
 
 At some point, enough tree leaves 
 are eaten to cause the tree to 
 produce new leaves — refoliation — 
 and this is bad for the tree. The 
 tree then behaves as if autumn and 
 spring have arrived together. The 
 remaining pieces of leaf and leaf 
 stems are shed just like they are in 
 autumn, but without a color 
 change. Then, the changes that 
 bring a tree from the resting state 
 to full leaf in the spring occur 
 again. In 2 to 3 weeks, new leaves 
 begin growing. This "spring again" 
 condition may be necessary for the 
 tree to survive, but because reserve 
 foods are used, it puts a 
 tremendous strain on the tree. 
 
 Even with the new leaves, the tree 
 is still at a disadvantage. The new 
 leaves are only half the original size 
 and are fewer in number than 
 before defoliation (fig. 5). The new 
 
 leaves are usually a lighter green, 
 which indicates that there is less 
 chlorophyll in them (chlorophyll is 
 the substance that converts light 
 energy from the sun to sugar 
 energy for the tree). The new 
 leaves are probably producing less 
 energy for the tree and have a 
 shorter growing season, too. These 
 problems may still be present the 
 following spring. 
 
 The shortage of energy causes the 
 tree to respond in several ways. 
 The most obvious is the dieback of 
 twigs and branches that occurs 
 especially during the winter months 
 and that becomes evident in the 
 spring. Usually the top twigs and 
 
 Figure 5. — Comparison of an 
 undefoliated tree {A ) with a 
 (Jct\)liatcd/reloliated tree («). 
 Notice that the leaves are a 
 lighter green, smaller, and tevser 
 in number on the refoliated tree. 
 
branches die first. When tip 
 branches die, old buds on the older 
 branches sprout; in severe cases 
 this sprouting occurs on the larger 
 branches and trunk and makes the 
 tree unattractive (fig. 6). 
 
 On living branches, the amount of 
 new twig growth is less than 
 normal — sometimes only one-tenth 
 as much as on undefoliated trees. 
 Internal growth is also affected: less 
 wood is produced in the annual 
 ring. This is not so important to 
 people who own trees mainly for 
 shade or beauty, but to foresters 
 who grow trees for wood products 
 it can mean considerable economic 
 loss. 
 
 Roots depend on the leaves for 
 food, too. When defoliation reduces 
 food production, many small feeder 
 roots can die. These roots absorb 
 minerals and most of the water 
 needed for tree growth. With fewer 
 feeder roots, fewer minerals and 
 less water are absorbed and sent to 
 the leaves, and food production by 
 the leaves is lowered even more. 
 
 Figure 6. — An oak tree shouing 
 the effects of defoliation and 
 sprouting of the tree in response 
 to branch death in the top of the 
 tree. 
 
3. How many years in succession 
 has defoliation occurred? 
 
 4. When during the year was the 
 tree defoliated? 
 
 One year of defoliation is bad, but 
 2 or 3 years of defoliation is worse. 
 Even defoliation that does not 
 cause the tree to refoliate is 
 harmful if it is repeated for several 
 years. A weak tree often suffers 
 after only one season of defoliation. 
 But even a healthy tree can die if 
 defoliated 2 or 3 years in a row, 
 especially if the tree refoliates each 
 time it is defoliated. A defoliated 
 tree begins the new season with a 
 considerable handicap, and a repeat 
 performance weakens the tree 
 further and lessens its chances for 
 survival. 
 
 No time is right for defoliation, but 
 the best time would be either very 
 early or very late in the growing 
 season. Early defoliation gives the 
 tree a longer time to recover before 
 natural autumn defoliation occurs. 
 Defoliation late in the season is less 
 harmful because the tree has 
 completed most of its growth, has 
 stored most of its food, and is 
 getting ready to do its normal 
 autumn shedding. Also, the tree 
 usually won't refoliate this late in 
 the season even if all the foliage is 
 eaten. However, several years of 
 defoliation even at these less 
 critical times can still be bad for the 
 tree. 
 
 The worst time for defoliation is 4 
 to 6 weeks after buds open in the 
 spring, when the tree is growing 
 rapidly and food reserves in the 
 shoots and roots are lowest. 
 Unfortunately, this is exactly when 
 the gypsy moth is doing most of its 
 feeding. With such low food 
 supplies, the tree cannot feed all its 
 branches and roots until new leaves 
 are formed; some die, and the tree 
 is weakened. 
 
5. What were the weather 
 conditions after defoliation? 
 
 How badl\ a tree is weakened 
 depends on ho\A quickly new leaves 
 are formed and how much food 
 they produce. Both are influenced 
 by the growing conditions or 
 weather. Too much rain during 
 refoliation miay set the stage for leaf 
 diseases caused by fungi (fig. 7). 
 and the tree may be defoliated 
 again in the same season. 
 
 Dry weather is just as bad. If a tree 
 lacks moisture during refoliation. 
 leaf growth is poor, and these small 
 
 leaves produce less food. If dr\ 
 weather continues, food production 
 is lowered because leaves need lots 
 of water to manufacture food. If 
 dryness occurs with high 
 temperatures, leaves may also be 
 scorched. 
 
 Figure 7. — Leaves of v^hite oak 
 showing symptoms of a fungus 
 disease. 
 
6. Did disease organisms and other 
 insects attack the tree? 
 
 The death blow to many trees after 
 defoliation comes from organisms 
 we call "opportunists." They take 
 advantage of the weakening effect 
 that defoliation has on a tree. If the 
 tree had not been defoliated, these 
 organisms would not succeed in 
 attacking the tree. One such 
 organism is a root-attacking fungus 
 called shoestring root rot, which 
 forms black shoelacelike stmctures 
 on the surface of the roots and in 
 the soil (fig. 8). Weak, dead, or 
 dying roots may provide entrance 
 places for this fungus, which can 
 
 then kill other roots. The fungus, 
 which grows in the food-and-water- 
 carrying tissues of the roots, 
 restricts the amount of water and 
 minerals that is carried to the 
 leaves and prevents food from 
 going to other roots (fig. 9). The 
 results are more dead roots and 
 greater water and nutrient 
 problems. 
 
 Figure 8. — Section of root 
 showing the black shoestringlike 
 structures of the shtiestring root 
 rot fungus growing on the bark 
 surface. 
 
 10 
 
Figure 9. — Dead oak tree with 
 uhite fans of the shoestring root 
 rot fungus grouing on the wood. 
 Fans were exposed by peeling off 
 the bark (right foreground). 
 
 11 
 
An insect that takes advantage of 
 primarily oak trees weakened by 
 defoliation is the twolined chestnut 
 borer (fig. 10). This insect attacks 
 the branches and trunk of the tree 
 and chews feeding tunnels in the 
 tissues that move food, water, and 
 minerals to the shoots and roots 
 (fig. 11). These tunnels prevent 
 water, food, and minerals from 
 moving to where they are needed, 
 which causes more leaves, 
 branches, and roots to die. 
 
 Figure 10. — Four growth stages 
 the tuolined chestnut tx>rer larva, 
 which tunnels in the bark and 
 uood of defoliated oak trees. 
 
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 The combination of the fungus in 
 the roots and borers in the shoots 
 will obviously result in a dead tree. 
 In many instances a tree v\ill die 
 rapidly, especially late in the 
 summer during hot. dry weather. 
 The leaves suddenly turn brown 
 and the tree dies (fig. 12). 
 
 Unfortunately both of these 
 organisms operate hidden beneath 
 the bark (figs. 9 and 1 1). and by the 
 
 time they are visible, the damage 
 has been done. Currently there is 
 no effective way to keep the fungus 
 from attacking the roots or to kill 
 the fungus once it enters the roots, 
 but the borer can be controlled 
 with insecticide. 
 
 Figure 11. — Dead oak tree 
 showing the feeding tunnels 
 created by lar\ ae of the twolined 
 chestnut borer. Tunnels were 
 exposed b\ removing the bark. 
 
 Figure 12. — Tree showing 
 symptoms of tuolined borer and 
 shoestring fungus attack. Leaves 
 brown suddenly dunng hot. dry 
 weather, usually in .August, and 
 the tree then dies. 
 
 13 
 
7. How healthy or vigoroas was the 
 tree before defoliation? 
 
 But even in the presence of 
 ■"opportunistic"' organisms and 
 after several successive years of 
 severe defoliation, a tree can 
 survive if it was in good health 
 when defoliated. Stresses such as 
 drought, soil compaction, or 
 disturbance during construction can 
 weaken a tree. These stresses 
 interfere indirectly with food 
 production and may reduce the 
 amount of stored food reserves or 
 even cause some twig and root 
 death. A tree weakened by stress 
 will be more vulnerable than a 
 healthy tree to the effects of gypsy 
 moth defoliation. 
 
 How can you help your tree 
 tolerate defoliation? First and 
 foremost, keep your tree healthy. 
 Water and fertilize it properly, 
 especially during stress conditions 
 such as drought. Try to avoid other 
 stress inducers such as soil 
 compaction, waterlogging, 
 competition from turf grasses, or 
 intrusions from driveways and 
 sidewalks. WTien you plant a ne\\ 
 tree, avoid these situations and 
 conditions that cause stress to the 
 tree. Give the root system adequate 
 growing room and mulch it for 
 proper aeration of the roots. If 
 possible, keep a mulched area 
 around the tree. Plant the proper 
 tree in the proper place, and 
 consult professionals if you aren't 
 sure. Cared-for trees are healthier 
 and will tolerate defoliation better. 
 
 Protect your tree from being 
 defoliated with carefully applied, 
 commercially safe insecticides. If 
 the tree is small, the caterpillars 
 
 can be picked off. If your tree gets 
 defoliated in spite of your efforts 
 and it re foliates, care for it during 
 refoliation. If moist conditions 
 prevail, be prepared to spray the 
 leaves with fungicide at the tlrst 
 sign of leaf disease. In very dry 
 weather, water your tree w hile it is 
 refoliating to help early leaf growth 
 and encourage healthy leaves. 
 Fertilize \our tree in the fall or 
 early spring before leaves appear to 
 help replace minerals lost during 
 defoliation. 
 
 Figure 13. — Adult hectic of the 
 twolined chestnut hoiei. uhich 
 lays eggs on the hark of oak trees 
 in late spring and eariy summer. 
 Note the tuo red-hroun lines on 
 the wing covers, from \shich the 
 horer gets its name. 
 
 14 
 
Acknowledgment 
 
 Borer attack can be reduced by 
 spraying the branches and trunk of 
 the tree with an insecticide 
 registered for use against borers. 
 Spraying should be done during the 
 month of June, when the beetle 
 stage of the borer is laying eggs on 
 the bark surface (fig. 13). 
 
 By applying these measures, your 
 tree should survive a defoliation 
 even if it loses all its leaves and 
 refoliates. But once your tree has 
 been defoliated, take extra 
 precautions not to let it happen 
 again next year. 
 
 The author thanks Dr. Robert 
 Talerico. Roger Zerillo. and 
 Richard Rollinson. Gypsy Moth 
 Program. Hamden. Conn., for 
 photographs of larvae and 
 defoliation, and Dr. Wilfred Cote. 
 International Paper Co.. Tuxedo 
 Park, N.Y., for photographs of the 
 twolined chestnut borer. 
 
 Issued January 1978 
 
 For Sale by the Superintendent of 
 
 Documents 
 
 U.S. Government Printing Office 
 
 Washington, D.C. 20402 
 
 Stock No. 001-000-3747-1 
 
 15 
 
UNIVERSITY OF FLORIDA 
 
 3 1262 08584 2937