Seedy Strawberry Problem

This problem usually usually occurs on berries that ripen in the mid and late season. Berries fail to size and color up properly and retain a hard "seedy" texture like a green/white strawberry. It was a major problem for us in 1994, 1996, and again in 1999. In 2001 we "solved" the problem.

In 1994 this problem occurred from Missouri to eastern Ohio in a narrow band roughly 50 to 100 miles north & south of I-70. After the fact analysis by Purdue and University of Illinois extension personnel "leaned" toward the explanation that a very small insect pest called the Eastern Flower Thrip was feeding on the Strawberry blossom and causing a deformity in the berry. Up to then, there had been no reports of thrip damage on strawberries for over 70 years.

In 1996 Lakeview Farms experienced another severe seedy berry problem but evidently very few other reports of this damage were made throughout the Midwest.

In 1998 I noticed relatively high populations (5 to 10 thrips per blossom) of these tiny insects feeding on our strawberry blossoms and ran a test spraying some strawberry blossoms and leaving some blossoms unsprayed. Neither the sprayed or unsprayed blossoms ever developed into seedy berries casting some doubt in my mind as to what the real culprit was. Soil moisture was relatively high.

In 1999 I noticed relatively low levels of thrips (2 to 4 ) feeding on the blossoms and elected not to spray based on the results I had seen the previous year. Seedy berry damage for 1999 unfortunately turned out to be especially severe! Soil moisture was relatively low.

During the 2001 strawberry bloom we again started to see thrip levels building in the field so we decided to repeat our study of 1998 where some strawberry rows we sprayed and others were left unsprayed.

The variety I chose for the study was Allstar primarily because we (unfortunately) have lots of experience with how it looks in "seedy berry" years like 1999, 1996, and 1994. Allstar is a relatively late berry compared to varieties like Earliglo, Northeaster, and Honeyoe and generally prone to much more damage. Seedy berry damage symptoms on Allstar are slightly different from all the other varieties we have grown -- besides the seedy appearance, poor color, smaller size, and dull finish Allstar (unlike other varieties) will usually have cracking like powdery mildew on west coast seedless grapes.

Thrip counts began April 27 roughly one week into the Allstar bloom period. Ten to twenty blossoms were placed into a sliding zip lock bag and three drops of ethyl acetate (nail polish remover) added to keep the thrips from moving around. It is my opinion that the ethyl acetate made counting easier and more accurate. The zip lock bag was put over a white sheet of paper and thrips counted with the aid of a 4X magnifying glass. While both adult and juvenile thrips were counted the juvenile population was never more than 20 to 30% of the total.

date	thrips per blossom in unsprayed check
4/27/01	0.1
4/28/01	0.2
4/29/01	no count
4/30/01	0.2
5/1/01	0.5
5/2/01	1.7
5/3/01	3.4
5/4/01	no count
5/5/01	3
5/6/01	no count
5/7/01	no count
5/8/01	13
5/9/01	24.2
5/10/01	25.2
5/11/01	33.3
5/12/01	27.8
5/13/01	no count

All but three check rows (300 feet each side by side) were sprayed with a Endosulfan/Diazinon insecticide mixture on May 2. Thrip counts in the sprayed area on May 3 were zero. I failed to check thrip counts in the sprayed area again until May 8 and was alarmed to see they had built up to 13.2 ( very close to the unsprayed control levels) so another application of Endosulfan (alone) was made on May 9. Once again, thrip counts in the sprayed area were essentially zero the day after spray. I made the mistake of putting the three check rows upwind of the sprayed controls so this might possibly have accounted for the rapid recovery of the thrips after the first insecticide application. Click here to view a picture of the layout.

By mid May, some of the Allstar were already showing the early orange coloration I have learned to associate with seedy berry years! Berry counts were initiated May 28 in two replicated 9 ft² plots marked off with pink phos tape. Our field supervisors (college kids) were instructed to pick " all berries that had no white showing" within the 9 ft² area before the area was opened to U-Pick customers. I personally made the individual berry determination of "seedy" versus "OK" then the samples were weighed and counted.

The small berry size of the 6/1/2001 and 6/5/2001 samples for both sprayed and unsprayed control plots is not representative of what is commercially saleable -- none of my U-Pick customers would pick ALL the ripe berries regardless of size. All this data is summarized in the table below:

		5/28/2001			6/1/2001			6/5/2001
	grams	count	grams/berry	grams	count	grams/berry	grams	count	grams/berry
No Spray Control -West		seedy picture OK picture			click here for picture			click here for picture
Seedy	272	34	8	114	27	4.2	14	2	7
OK	272	38	7.2	123	23	5.4	182	30	6.1
% Seedy by count		55%			54%

No Spray Control - -East		seedy picture OK picture			click here for picture			click here for picture
Seedy	363	42	8.6	141	25	5.6	23	5	4.6
OK	272	32	8.5	77	13	5.9	222	30	7.4
%Seedy by count		57%			66%

Sprayed -West		click here for picture			click here for picture			click here for picture
Seedy	0	0		0	0		0	0
OK	681	77	8.8	418	78	5.4	245	41	6
%Seedy by count

Sprayed - East		click here for picture			click here for picture			click here for picture
Seedy	0	0		0	0		0	0
OK	1362	102	13.3	504	89	5.7	477	61	7.8
%Seedy by Count

1. Why did the last counts in the no spray controls show dramatic improvement? I have never seen thrip damage improve as the season progressed. Even though we did not do a formal count on our last day of the season, I could find no seedy berries in any of the unsprayed rows! The only environmental difference between the mid bloom versus late bloom Allstar that I can recall is that a relatively dry soil condition changed rapidly to a relatively wet soil condition.