United States

{.@) Department of

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P* I- Forest Service

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 Southern Forest

Research Note

Experiment Station so-307

Mav 1984

Nitric Acid and Benomyl Stimulate Rapid Height Growth

of Longleaf Pine

A. G. Kais, R. C. Hare, and J. P. Barnett

SUMMARY INTRODUCTION

Rapid height growth of longleaf pine seedlings, important to production of uniform, even-aged stands, can be

promoted by controlling brown-spot needle blight and

weed competition, and by increasing soil fertility. Root

systems of container-grown longleaf pine seedlings were

dip-treated in either benomyl/clay mix (10 percent a.i.

benomyl) or clay control and planted in scalped rows that

had been treated with various levels of nitric acid (0, 4, or

8 percent). After one growing season in the field, seedlings were evaluated for survival, brown spot infection,

and vigor; plots were evaluated for weed competition.

The benomyl root-dip treatment improved seedling survival, controlled brown spot infection, and promoted

growth of outplanted seedlings in the first year. For the

same period, treatment of soil with nitric acid improved

seedling survival and vigor and significantly reduced the

amount of competing vegetation. The combined use of

benomyl and nitric acid resulted in the most rapid height

growth.’

Additional keywords: Brown-spot needle blight,

Scirrhia acicoh (Dearn.) Siggers, fertilizer, herbicide, disease control, Pinus palustris.

‘This publication reports research involving nitric acid as a pesticide. It

does not imply that the use discussed has been registered. All uses of

pesticides must be registered by appropriate State and/or Federal

agencies before they can be recommended.

Caution: Concentrated nitric acid is extremely caustic and will cause

severe burns to skin or eyes. It also produces toxic fumes. Avoid prolonged inhalation and immediately rinse any spills on skin or clothing

with copious amounts of water. Always add acid to water, not vice

versa.

Longleaf (Pinus palustris Mill.) pine seedlings possess

a temporary dwarf habit of growth which has been a

major obstacle in its regeneration. Partly as a consequence, longleaf has been supplanted by other pine

species and now occupies only about 25 percent of the

area it once dominated (Mann 1969). The initiation of

rapid height growth of longleaf pine is normally delayed

until the seedling has passed through a preliminary

period of root and foliar development known as the grass

stage (Wahlenberg 1946). This condition is an inherent

seedling trait under genetic control, although the length

of time seedlings remain in this grass stage is strongly

influenced by such environmental influences as brownspot needle blight, competition from other plants, and low

soil fertility (Brown 1964). These may delay height growth

up to 15 or 20 years (Bruce 1958, Dorman 1976). Cultural practices such as the control of brown-spot needle

blight by chemicals or fire (Kais et al. 1981 a, 1981 b), the

control of weed competition (Bruce 1958, Mann 1969,

Pessin 1944) and fertilization (Hinesley and Maki 1980,

Lewis 1977, Schmidtling 1973, Smith and Schmidtling

1970) have all resulted in earlier height growth.

Longieaf pine has excellent form, good wood qualities,

and resistance to fusiform rust caused by Cronartium

quercuum (Berk.) Miyabe ex Shirai f. sp. fusiforme. Yet,

because of the problems associated with the grass stage

during its early development, it is not planted extensively.

Seedlings in a prolonged grass stage are frequently killed

by brown-spot needle blight and weed competition.

However, brown spot is primarily a disease of the grass

stage, and a method of stimulating early height growth by

controlling both brown spot and weeds would reduce

losses, ensure a more uniform stand, and make longleaf

pine more attractive for reforestation.

Southern Forest Experiment StationR-10210 U.S. Postal Services Bldg., 701 Loyola Avenue, New Orleans, La. 70113

Forest Service, U.S. Department of Agriculture.

Serving Alabama, Arkansas, Louisiana, Mississippi, E. Oklahoma, Tennessee, E. Texas, Puerto Rico, U.S. Virgin Islands

1
Brown spot has been effectively controlled by benomyl used as a root dip treatment before outplanting (Kais

et al. 1981a, 1981 b). A 4 percent nitric acid solution has

been used to control weed competition and to provide

nutrition to pine seedlings in the form of available nitrogen

(Hare 1984). A single nitric acid application helps overcome growth inhibition caused by low soil fertility and

weed competition. It has pre-emergence activity when

sprayed on bare soil and post-emergence activity when

used as a directed spray on emerging weeds. Treated

areas remain essentially weed-free during one growing

season without any significant injury to pine seedlings.

The purpose of this study was to stimulate rapid height

growth of containerized longleaf pine seedlings outplanted in the field. Three well-known growth inhibitors

were studied: (1) brown-spot needle blight, (2) low soil

fertility, and (3) weed competition. Benomyl root dip treatments were used to control the brown spot, while nitric

acid soil application was used to provide nitrogen-nutrition and control weed competition. Previous tests had

indicated that containerized longleaf pine seedlings

planted by machine had excellent survival rates,

MATERIALS AND METHODS

Longleaf pine seeds were germinated in Leach

Supercell containers at Alexandria, Louisiana, in May

1981. These cells, 1 l/2 inches in diameter and 81/2 inches

in length, each contained approximately 10 cubic inches

of an equal mix of vermiculite and peat moss. Peters

Water Soluble Plant Fertilizer (20-l 9-l 8 NPK) was applied

at 150 ppm nitrogen weekly. Containers with seedlings

were transferred to a greenhouse at Gulfport, Mississippi,

in August 1981. They were next transferred to a lathhouse at Saucier, Mississippi, on November 5, 1981, and

held there until outplanting in January 1982. At planting

time, compressed air was applied to the drain holes of the

containers and seedlings were readily removed in one

piece.

The field test was installed as a randomized complete

block design consisting of 3 nitric acid levels x 2 root-dip

treatments x 6 blocks x 30 seedlings for a total of 1,080

seedlings. Treatment row locations had been prepared

by scalping 3-foot swaths in July 1981. The scalped rows

were treated with 0, 4, or 8 percent nitric acid (HNO,) in

water on August 3, 1981. Solutions were prepared by

adding 65 percent technical grade HNO, to water in a

portable stainless steel tank. A long rubber hose with a

‘The mention of a company or trade name does not imply endorsement

by the USDA.

fan rose sprinkler and shut-off valve attached to the tank

was used to moisten the soil surface and any emergent

weeds on the scalped plots. Approximately 2.5 gallons of

solution were applied to treatment areas of 30 x 2 feet

(60 ft”).

Seedlings were machine planted with a Whitfield

planter on January 27 - 28, 1982. The 180 seedlings per

block were divided into two groups of 90 seedlings each.

One group was dipped in plain kaolinite clay and the

other into a kaolinite clay-benomyl mixture (10 percent

a.i. benomyl). Thirty seedlings of each group were then

planted at 3-foot intervals in one of the three different

acid-soil treatment plots. Individual treatments and treatment rows were separated by a IO-foot spacing; blocks

were separated by a 20-foot border. Naturally occurring

longleaf pine seedlings in the area surrounding the planting were heavily infected with brown-spot needle blight.

In November 1982, seedlings were evaluated for survival, brown-spot infection, and vigor. All plot surfaces

were rated for degree of weed competition at the same

time. Brown-spotlinfection was determined for each seedling by a visual estimate of the percent of needle tissue

area killed by the disease. Vigor was rated by using a

vigor index: 1 = poor, 2 =fair, 3= good, and

4= excellent. Weed competition was evaluated with a

competition index: 1 = none, 2 = slight, 3 = moderate,

and 4=severe. Data were evaluated by an analysis of

variance. Treatment means were compared by means of

Duncan’s Multiple Range Test at the 0.05 level.

RESULTS

First-year field survival of seedlings varied from 66.3 to

88.0 percent (table 1). Significant survival differences of

seedlings depended on the specific treatment combinations. There was an increase in survival with an increase

in nitric acid dosage applied to the plots and a significantly greater survival rate for the seedlings treated with

benomyl than those treated with plain clay dips. Survival

of seedlings not treated with benomyl was significantly

increased only at the higher level of nitric acid application.

Seedlings treated with benomyl had only 3.1 to 4.0

percent brown-spot infection, compared to the corresponding clay-treated seedlings that had from 28.3 to

39.6 percent. There were no infection differences on

seedlings treated with benomyl and the three different

acid-water treatments. However, clay-dipped seedlings

had less infection following the 4 and 8 percent nitric acid

treatments than did the seedlings in soil treated with

water.

A. G. Kais and R. C. Hare are Research Plant Pathologist and Research Plant Physiologist, respectively, at the Southern Forest Experiment Station,

Forest Service-USDA, Gulfport, Mississippi. J. P. Barnett is Supervisory Research Forester at the Southern Forest Experiment Station, Forest Service

-USDA, Pineville, Louisiana.

2
Table 1 .-Survival, infection, and vigor of containerized longleaf pine seedlings and weed control after 1

year in the field

Dip and acid

treatments

BenomyllClay

0 nitric acid

4% nitric acid

6% nitric acid

Brown-spot

Survival infection Vigor index’ Weed index1

__________ ______________ __________________ ______percent ________________________________________ ____._ _

79.7 abc) 3.8 c 3.8 c 2.1 a

74.3 bed 4.0 c 3.7 a b 1.3 b

88.0 a 3.1 c 3.9a 1.2 b

Mean 80.7 3.6 3.6 1.5

Clay

0 nitric acid

4% nitric acid

6% nitric acid

Mean

66.3 d 39.6 a 2.6 d 2.4 a

67.8 c d 28.3 b 3.3 b c 1.3 b

85.6 a b 29.6 a b 3.6 abc 1.1 b

73.2 32.5 3.2 1.6

‘Vigor index; 1 = poor, 2 = fair, 3 = good, and 4 = excellent,

2Weed competition index; 1 = none, 2 = slight, 3 = moderate, and 4 = severe.

‘For each parameter, values in the same column followed by the same letter are not significantly different

(P = 0.05). Each treatment value is the mean of 6 blocks of 30 seedlings each.

Figure 1 .--Effect of benomyl and nitric acid treatment on longleaf pine p/ants. Left: In contra/, scalping iS

evident but some weeds appear; p/ants are not large, as growth is limited by brown-spot

needle blight infection, low soil nitrogen, and weed competition. Right: Treated plants are

larger because brown-spot disease and weed competition are controlled and there is more

soil nitrogen available.

3
Both the nitric acid-soil treatments and the benomyl

root-dip treatments resulted in higher seedling vigor (table 1). Seedling vigor was greatest with the highest rate of

HNO, (8 percent), and poorest with the water control.

Seedlings dipped in benomyl at the time of outplanting

were significantly more vigorous than seedlings treated

with plain clay. Combinations of benomyl and HNO,

generally had the highest survival and vigor with the least

brown spot and weeds (table 1, fig. 1).

The weed competition index, including both grass and

broadleaf weeds, was greatest where no nitric acid was

applied to the soil (table 1). All nitric acid treatments significantly reduced the index below that of the control. The

benomyl root treatment had no effect on weeds.

DISCUSSION

Longleaf pine survival, growth, and overall development was excellent in the 1 O-cubic-inch containers. Root

dipping of the seedlings was a simple operation and the

benomyl-clay mixture adhered tenaciously to the root cylinder. Furthermore, seedlings retained their root cylinder

configuration and benomyl-clay coverage during the

machine planting operation performed with the Whitfield

tree planter. Survival, which was lower than expected,

was probably reduced by unseasonably cold temperatures during the time seedlings were held in the lathhouse

and later, after they were outplanted in the field.

The positive benomyl effect on survival and growth

presumably resulted from effective disease control, permitting normal growth.

The nitric acid effect on both survival and growth of

seedlings was twofold: direct, in that it provided readily

usable nutrition to the seedlings, and indirect, in that it

eliminated plants competing with the longleaf pine seedlings for available nutrients and moisture.

The greatest survival and vigor of longleaf pine seedlings occurred with the 8 percent HNO, treatment, with or

without benomyl (table 1). However, the 4 percent and 8

percent HNO, sprays were equally effective for weed

control. The 4 percent spray applied either just before

planting or 2 weeks after would require less material, and

this timing would provide more available nitrogen to the

plants. These applications can be limited to a l-foot radius around each seedling. Care must be taken to protect

pine foliage from direct contact with diluted nitric acid if

applied after planting.

Applied at a rate of 2.5 gallons/60 ft*, the cost per

seedling of the nitric acid needed for a 4 percent spray

applied in a l-foot radius around each tree would be

$0.07. Cost of the acid material needed per acre of a

longleaf planting with a lo- by IO-foot spacing would be

approximately $30 and of a 6- by 8-foot spacing about

$63 per acre. A 4 percent HNO, treatment of the lo- by

IO-foot planting would provide approximately 1.8 kg of

nitrogen per acre, while treatment of a 6- by 8-foot planting would provide 3.8 kg of nitrogen per acre. In both

instances, 4.2 g of nitrogen are provided per seedling.

The combined use of benomyl and nitric acid could

4

overcome some of the persistent problems that are associated with the culture of longleaf pine. The growth stimulation following the simultaneous control of competing

vegetation and brown-spot needle blight plus the addition i

of available nitrogen reduce the time required for root

development, allowing seedlings to start height growth

sooner. Longleaf pine seedlings receiving the treatments

should be out of the grass stage within 2 to 3 years after

outplanting. This in turn should produce the uniform

stands that have been difficult to attain in the past and

which are so crucial for longleaf pine regeneration in the

future.

LITERATURE CITED

Brown, C. L. The seedling habit of longleaf pine. Report

No. 10. Georgia Forest Research Council. 1964: 68 p.

Bruce, David. Effect of low competition on longleaf pine

seedling growth. In: Proc. Sot. Am. Foresters, 1958;

Salt Lake City, UT. 1958: 151 - 153.

Dorman, K. W. The genetics and breeding of southern

pines. Agric. Handb. 471. Washington, DC: U.S.

Department of Agriculture, Forest Service. 1976. 407

P.

Hare, R. C. EL-506-An effective seedlings growth retardant for dwarfing southern pine. Canadian Journal of

Forest Research. 1984. In press.

Hinesley, L:Eric; Maki, T. E. Fall fertilization helps longleaf pine nursery stock. Southern Journal of Applied

Forestry. 4: 132 - 135; 1980.

Kais, A. G.; Cordell, C. E.; Affeltranger, C. E. Control of

brown-spot needle blight on longleaf pine by benomyl

root-dip treatment (Abstr.) Phytopathology. 71:

884 - 885; 1981 a.

Kais, Albert G.; Snow, Glenn A.; Marx, Donald H. The

effects of benomyl and Pisolithus tinctorius ectomycorrhizae on survival and growth of longleaf pine seedlings Southern Journal of Applied Forestry. 5:

189-195; 1981b.

Lewis,,Clifford E. Longleaf pine responds through age 15

to early fertilization. Res. Note SE-239. Asheville, NC;

U.S. Department of Agriculture, Forest Service, Southeastern Forest Experiment Station; 1977. 7 p.

Mann, William F., Jr. At last-longleaf pine can be

planted successfully. Forest Farmer. 28: 6- 7,

18-19; 1969.

Pessin, L. J. Stimulating the early height growth of longleaf pine seedlings. Journal of Forestry. 42: 95-98;

1944.

Schmidtling, R. C. Intensive culture ‘increases growth

without affecting wood quality of young. southern

pines. Canadian Journal of Forest Research. 3:

565 - 573; 1973.

. Smith, L. F.; Schmidtling, R. C. Cultivation and fertilization

speed early growth of planted southern pines. Tree

Planters’ Notes. 21(l): 1 - 3; 1970.

Wahlenberg, W. G. Longleaf pine. 1st ed. Washington,

DC: Charles Lathrop Pack Forestry Foundation; 1946.

429 p.

* U.S. GOVERNMENT PRINTING OFFICE: 1984-769-089:22