After a down month of June for the S&P 500, tracked by the SPDR S&P 500 ETF Trust, the market index couldn’t fare any better in July.

Strategist Ryan Detrick warns S&P 500 investors to brace for the 'worst two months' in August and September after a weak June and July.

After a down month of June for the S&P 500, tracked by the SPDR S&P 500 ETF Trust, the market index couldn’t fare any better in July.