ype. Members of this class must have an uninterrupted dark period in order to
5 ; the briefest interruption by light usually is sufficient to prevent flowering.
garcane it has been established that 50-foot-candle-minutes of incandescent
s the minimum quantity of light required to inhibit flowering.
After determining that night interruption from September 1st to 20th would
hemicals. Because temperature cannot be controlled in the field and be-
ished with the approval of the Director as Paper No. 161 in the Journal Series of the
tation, Hawaiian Sugar Planters' Association, Honolulu, Hauiaii.
114
AGRICULTURE
the field soils so that the timing of the last irrigation round before initiation period
will bring the cane to the proper moisture stress in early September (4-5 joint moisture of 85.5%) (Tanimoto, 1961).
2. Rain might nullify any successful control.
3. On a field-scale basis, there is the problem of resuming irrigation in all fields
simultaneously at the end of the stress period. Depending upon the water supply and
the extent of the area under control, over-dry conditions may result in some areas.
The first potentially useful commercial chemical was maleic hydr~zidewhich, a t best,
gave about 60% control. Rapid developments led to the establishment of monuron
(3-9-chlorophenyl-I,I-dimethylurea)
as the chemical of choice, and later included
When applied properly, these chemdiuron (3-[3,4-dichlorophenyll-I,I-dimethylurea).
icals give virtually complete control of tasseling in H 37-1933, a heavy-tasseling
variety in most areas.
Continued research in tassel control has led to the present recommendations
for Hawaiian plantations :
I. Monuron or diuron applied as a foliar spray at the rate of 5 pounds per acre
(4 pounds of active material) during the period September 6 to 14.
2. Withholding of irrigation water in sufficient time to reduce the tissue moisture of the 4th and 5th joints to 85.5% on September IQ and a return of the water
on September 14.
In order to gain acceptance, a new chemical would have to have one or more of
the following qualifications :
I. Greater activity.
2. Less cost.
3. Greater leeway in timing.
4. Less cane toxicity.
While the current recommended practices are effectivein a large percentage of
cases, they are not completely foolproof. For this reason, efforts have been continued
to find new and better methods of control or more efficient chemicals for control.
Tests at this Station in 1960 indicated that the compound 1.1'-ethylene-2,~'dipyridylium dibromide gave good tassel control. At first called FB-2, the preparation
is now available under the trade names Diquat and Reglone, and as the equally
effective dichloride salt. Dosages originally tested (2 pounds per acre) were too high,
the growth of the stalks was adversely affected and, in many instances, the cane was
completely billed. Further testing in 1961 showed that rates as low as 0.125 pound
per acre of the ionic form (equivalent to 0.25 pound per acre of the salt form) could be
effective, malting it one of the most active compounds yet evaluated. (All dosages of
Diquat in this report wiIl be expressed on the basis of the ionic form rather than the
salt form.) These results led t o more extensive testing in 1962 a t the Experiment Station, and to cooperative tests at Kahuku Plantation Company on the island of Oahu
and at Hawaiian Commercial & Sugar Co., Ltd. on the island of Maui. In these tests,
several aspects of the probleni were studied: amount of active material, rate and
timing of application, formulation, degree of phytotoxicity, age and condition of the
crop, and geographical location of the test fields. Both the heavy-tasseling variety
H 37-1933 and the lighter-tasseling variety H 50-7209 were included.
The HSPA experiment at ~ a h u l t uPlantation Company was designed t o com-
T, TANIMOTO, L. G. NICKELL
pare two rates (0.25 and 0.125 pound per acre) applied by airplane on a single date
(september 7) in 15 gavons of water per acre on H 37-1933 The test included three
on plots of about 0.5 acre. Observations and tassel counts made in January 1963 showed considerable variation in control among the individual plots. This
can be accounted for by the wind and the flight pattern during application.
Tasseling was reduced from 72% in the control to 33% in the treated plots affectedby
wind and flight pattern; tasseling was reduced to 5% in the treated plots not so
affected. There were no apparent differences between the two rates.
On September 10, Kahultu Plantation Company sprayed a much larger area
adjacent to this test with 0.25 pound of Diquat in 7 gallons of water per acre and
obtained very effective control. Tassel counts made March 27, 1963, showed 2%
tasseling in the sprayed areas compared to 70% tasseling in the unsprayed area. The
percentage of tasselingin theunsprayed area is low in this case because the count made
at this time included suckers which were too small to flower at the time of application (the previous September). Such false counts are commonly obtained when stalks
capable of flowering are not marlted at time of application.
The test at Hawaiian Commercial & Sugar Co., Ltd. was designed primarily to
determine the effect of different dates of application upon control. This test was in a
traditionally heavy-tasseling area with H 50-7209, which was about I year old.
Bloclts of about 10 acres each were treated with 0.25 pound of Diquat in 7 gallons of
water per acre on four separate dates: August 31, September 7, September 14, and
September 22. Tassel counts made the following February 14th showed these results :
Date sprayed
Tassel
September 7
September 14
September 22
14
13
23
(%)
'~ncreasein non-tassel
over control (%)
26
IG
Although the control of tasseling is not as great as in the heavy-tasseling H 37-1933
at Kahuku, there is considerable control in the lighter-tasseling H 50-7209 The similarity of results over a 3-week period suggests that the effective interval over which
Diquat might be used could be greater than the effective period for current materials.
Yield results are not presented, as this test could not be harvested on schedule
because of operational difficulties. The possibility of varietal differences in growth
responses to Diquat, with H 50-7209 being sensitive, has been suggested in other
tests. This possibility is being investigated.
Harvest results obtained in March 1964 of the HSPA experiment at Kahultu
Plantation Company are as follows:
Replicates
Tons canelacre
Tons pol*/acre
11.4
13.2
13.5
* "Pol" is the angular rotation of the plane of polarization as measured with a sacchari'neter. Its scale readings are in terms of sucrose percentages when the rotation of a normal we~ght
of sucrose in IOO ml is read with a zoo-mm tube. The pol percentage of a solution will equal sucrose
Percentage, determined analytically, if sucrose is the only substance in solution that rotates the
plane of polarization.
i'
AGRICULTURE
The plantation test area a t Kahuku Plantation Company gave the following results:
Treatment
Replicates
Tons canelacre
Tons pollacre
These results show that Diquat, when properly applied, can effectively control
tasseling in certain sugarcane varieties. Its advantage over currently used chemicals
is the low levels of material needed, which cuts the total cost per acre for control sub-
SUMMARY
Two methods of tassel control in sugarcane are currently recommended and used by plantations in
Hawaii: (I) foliar apbllcation of monuron or diuron a t the rate of four pounds of active material
per acre during the period September 6 to 14, and (2) withholding of irrigation water to reduce
tissue moisture to certain specified levels a t the time of initiation. This paper presents recent work
with Diquat (~,~'-ethylene-z,z'-di~~rid~lium
dibromide) showing effective tassel control and
increased sugar yields in the heavy-tasseling variety H 37-1933 a t the concentration of 0.25 pound
of the cation form per acre. The resultant cut in cost per acre for control is substantial.
REFERENCES
ALLARD,
H. A. (1938) Complete or partial inhibition of flowering in certain plants when days are
too short or too long. J . A g r . Research, 57 : 775-789.
GARNER,
W. W. AND ALLARD,H. A. (1920), Effect of the relative length of day and night and
other factors of the environment on growth and reproduction in plants. J . A ~ YResearch,
.
18: 553-606
TANIMOTO,
T. (1961), 4-5 joint as indicators of moisture tension of the sugar cane plant. Repis.
Hawaiian Sugar Technologists, 20th Meeting, pp. 265-274.
Discussion
J. L. Du TOIT(SO.Africa) : We found experimentally that the correct timing of nitrogen application can reduce flowering significantly. Thus in an experiment where certain plots received 50 lbs.
per acre N in February, the average flowering per lot was 59; where t h e treatment was not given,
the average was 364.
M. SHAW(Jamaica) : You state that water withdrawal prevents flowering. It also has been stated
that heavy rainfall before a cool spell prevents flowering. 1s this related t o leaching of nitrogen ?
L. B. NICIZELL
(Hawaii) : The withdrawal of water a t the right time can prevent flowering, and
that is in fact done on several plantations. It can be an excellent practice if YOU are short of water.
M. I. TIO (Puerto Rico) : Do the dates you mention have a relation t o t h e normal floral induction
DR. NICICELL:
Yes, and under our conditions it is important t h a t t h e timing be exact. The time
spread is not the same for all chemicals and some are very critical.
BULLOCIC
(Dominican Republic) : What was the total liquid applied per acre ? We found that using
Reglone on B. 42231 and NCO 310 applied during the second weel< i n September an 80% control
was obtained using 4 and 8 gallons total liquid per acre.
DR. NICICELL:
We found between 7 and 10 gallons are required. From 10 t o 20 gallons the control
is not so good. The Diquat should be applied as a fine mist which penetrates the spindle and affects the young leaves, but the field soon again assumes a normal appearance.
T. CHINLOY
(Jamaica) : Has the inhibition of tasseling resulted i n a n increase in Sucrose content
and sugar production per acre ?
DR. NICKELL:The yield of sugar per acre has been increased b y I or 2 tons but I do not lcnow
whether the sucrose content of the cane was also improved.
LINDSAY(Peru) : Has an economic evaluation of sugar losses been made when cane flower ? If so,
T. TANIMOTO, L. G. NICKELL
117
how much sugar do you estimate is lost and does this loss warrant expensive control of flowering ?
DR. NICIZELL
: I have already referred to the losses, but it can be even up t o 4 tons sugar per acre.
The cost of treatment amounts t o $5 per acre. It is up t o management to decide whether this
insurance is warranted. Hawaii grows a two year crop and tasseling during the second season does
not matter so much, but it is tasseling during the first year that we want to prevent.
E. HERNANDEZ
(Puerto Rico) : I s there any evidence that environmental factors (temperature
and humidity) might have an influence on the phytotoxicity effect of Diquat on sugarcane ?
DR. NICKELL:There is some evidence but the whole matter is now being investigated; and when
the experiments are completed, we will have the answers.
p. KNOWLES
(Jamaica) : Are there varieties which do not flower significantly in their first season ?.
DR.NICKELL.Yes. There are varieties which do not flower a t all, but these may not be the most
efficient sugar producers in other aspects.
R.R. PANJE(India) : The authors refer to the geographical location, and I would like to point out
that we have found t h a t flowering was delayed by about 21 days per degree of latitude away from